.\"
.\" David Korn
.\" AT+T Bell Laboratories
.\"
.\" @(#)sh.1 (research!dgk) 12/28/93
.\"
.nr Z 0 \" set to 1 when command name is ksh rather than sh
.nr Y 0 \" set to 1 for R&D UNIX
.if \nY=1 .nr Z 1
.ds OK [\|
.ds CK \|]
.ds ' \s+4\v@.3m@\'\v@-.3m@\s-4
.ds ` \s+4\v@.3m@\`\v@-.3m@\s-4
.if \nZ=0 .TH SH 1
.if \nZ=1 .TH KSH 1 "User Environment Utilities" "RDS Standard"
.SH NAME
.if \nZ=0 sh, rsh \- shell, the
.if \nZ=1 ksh, rksh \- KornShell, a
standard/restricted command and programming language
.SH SYNOPSIS
.if \nZ=0 .B sh
.if \nZ=1 .B ksh
[
.B \(+-abcefhikmnoprstuvxCD
] [
.B \-R
file ] [
.B \(+-o
option ] .\|.\|. [
.B \-
] [ arg .\|.\|. ]
.br
.if \nZ=0 .B rsh
.if \nZ=1 .B rksh
[
.B \(+-abcefhikmnoprstuvxCD
] [
.B \-R
file ] [
.B \(+-o
option ] .\|.\|.  [
.B \-
] [ arg .\|.\|. ]
.SH DESCRIPTION
.if \nZ=0 .I Sh
.if \nZ=1 .I Ksh
is a command and programming language
that executes commands read from a terminal
or a file.
.if \nZ=0 .I Rsh
.if \nZ=1 .I Rksh
is a restricted version of the 
.if \nZ=0 standard 
command interpreter
.if \nZ=0 .IR sh ;
.if \nZ=1 .IR ksh ;
it is used to set up login names and execution environments whose
capabilities are more controlled than those of the standard shell.
See
.I Invocation
below
for the meaning of arguments to the shell.
.SS Definitions.
A
.I metacharacter
is one of the following characters:
.PP
.RS
\f3;   &   (   )   \(bv   <   >   new-line   space   tab\fP
.RE
.PP
A
.I blank
is a
.B tab
or a
.BR space .
An
.I identifier
is a sequence of letters, digits, or underscores
starting with a letter or underscore.
Identifiers are used as components of
.I variable
names.
A
.I vname
is a sequence of one or more identifiers
separated by a \fB\s+2.\s-2\fP and optionally preceded
by a \fB\s+2.\s-2\fP.
Vnames are used as function and variable names.
A
.I word
is a sequence of
.I characters
from the character set defined by the current locale,
excluding non-quoted
.IR metacharacters .
.PP
A 
.I command
is a sequence of characters in the syntax
of the shell language.
The shell reads each command and
carries out the desired action either directly or by invoking
separate utilities.
A built-in command is a command that is carried out by the
shell itself without creating a separate process.
Some commands are built-in purely for convenience
and are not documented here.
Built-ins that cause
side effects in the shell environment and 
built-ins that are found before performing a
path search (see
.I Execution
below)
are documented here.
For historical reasons, some of
these built-ins behave differently than
other built-ins and are called
.IR "special built-ins" .
.SS Commands.
A
.I simple-command
is a list of variable assignments
(see
.I "Variable Assignments"
below)
or a sequence of
.I blank
separated words
which may be preceded by a list of variable assignments
(see
.I Environment
below).
The first word specifies the name of the command to
be executed.
Except as specified below,
the remaining words are passed as arguments
to the invoked command.
The command name is passed as argument 0
(see
.IR exec (2)).
The
.I value
of a simple-command is its exit status; 0-255
if it terminates normally; 256+\f2signum\^\fP if
it terminates abnormally (the name of the signal corresponding
to the exit status can be
obtained via the
.B \-l
option of the
.B kill
built-in utility).
.PP
A
.I pipeline
is a sequence of one or more
.I commands
separated by
.BR \(bv .
The standard output of each command but the last
is connected by a
.IR pipe (2)
to the standard input of the next command.
Each command,
except possibly the last,
is run as a separate process;
the shell waits for the last command to terminate.
The exit status of a pipeline is the exit
status of the last command.
Each pipeline can be preceded by the
.I "reserved word"
.B !
which causes the exit status of the pipeline to become
0 if the exit status of the last command is non-zero, and
1 if the exit status of the last command is 0.
.PP
A
.I list
is a sequence of one or more
pipelines
separated by
.BR ; ,
.BR & ,
.BR \(bv& ,
.BR && ,
or
.BR \(bv\|\(bv ,
and optionally terminated by
.BR ; ,
.BR & ,
or
.BR \(bv& .
Of these five symbols,
.BR ; ,
.BR & ,
and
.B \(bv&
have equal precedence,
which is lower than that of
.B &&
and
.BR \(bv\|\(bv .
The symbols
.B &&
and
.B \(bv\|\(bv
also have equal precedence.
A semicolon
.RB ( ; )
causes sequential execution of the preceding pipeline; an ampersand
.RB ( & )
causes asynchronous execution of the preceding pipeline (i.e., the shell does
.I not
wait for that pipeline to finish).
The symbol
.B \(bv&
causes asynchronous execution of the preceding pipeline
with a two-way pipe established to the parent shell;
the standard input and output of the spawned pipeline
can be written to and read from by the parent shell
by applying
the redirection operators
.B <&
and
.B >&
with arg
.B p
to commands and by using
.B \-p
option of
the built-in commands
.B read
and
.B print
described later.
The symbol
.B &&
.RB (\| \(bv\|\(bv \^)
causes the
.I list
following it to be executed only if the preceding
pipeline
returns a zero (non-zero) value.
One or more new-lines may appear in a
.I list
instead of a semicolon,
to delimit a command.
.PP
A
.I command
is either a simple-command
or one of the following.
Unless otherwise stated,
the value returned by a command is that of the
last simple-command executed in the command.
.TP
\f3for\fP \f2vname\^\fP \*(OK \f3in\fP \f2word\^\fP .\|.\|. \*(CK \f3;do\fP \f2list\^\fP \f3;done\fP
Each time a
.B for
command is executed,
.I vname
is set to the next
.I word
taken from the
.B in
.I word
list.
If
.BI in " word\^"
\&.\|.\|.
is omitted, then
the
.B for
command executes the \f3do\fP \f2list\^\fP once for each positional parameter
that is set starting from
.B 1
(see
.I "Parameter Expansion"
below).
Execution ends when there are no more words in the list.
.TP
\f3for ((\fP \*(OK\f2expr1\^\fP\*(CK \f3;\fP \*(OK\f2expr2\^\fP\*(CK \f3;\fP \*(OK\f2expr3\^\fP\*(CK \f3))\fP \f3;do\fP \f2list\^\fP \f3;done\fP
The arithmetic expression
.I expr1
is evaluated first
(see
.I "Arithmetic Evaluation"
below).
The arithmetic expression
.I expr2
is repeatedly evaluated until it evaluates to zero and when non-zero,
.I list
is executed and the arithmetic expression
.I expr3
evaluated.
If any expression
is omitted, then it behaves as if it evaluated to 1.
.TP
\f3select\fP \f2vname\^\fP \*(OK \f3in\fP \f2word\^\fP .\|.\|. \*(CK \f3;do\fP \f2list\^\fP \f3;done\fP
A
.B select
command prints on standard error (file descriptor 2) the set of
.IR word s,
each preceded by a number.
If
.BI in " word\^"
\&.\|.\|.
is omitted, then
the
positional parameters starting from
.B 1
are used instead
(see
.I "Parameter Expansion"
below).
The
.SM
.B PS3
prompt is printed
and a line is read from the standard input.
If this line consists of the number
of one of the listed
.IR word s,
then the value of the variable
.I vname
is set to the
.I word
corresponding to this number.
If this line is empty, the selection list is
printed again.
Otherwise the value of the variable
.I vname
is set to
.IR null .
The contents of the line read from standard input is
saved in
the variable
.SM
.BR REPLY .
The
.I list
is executed for each selection until a
.B break
or
.I end-of-file
is encountered.
If the
.SM
.B REPLY
variable is set to
.I null
by the execution of
.IR list ,
then the selection list is printed before
displaying the
.SM
.B PS3
prompt for the next selection.
.TP
\f3case\fP \f2word\^\fP \f3in\fP \*(OK \*(OK\f3(\fP\*(CK\f2pattern\^\fP \*(OK \(bv \f2pattern\^\fP \*(CK .\|.\|. \f3)\fP \f2list\^\fP \f3;;\fP \*(CK .\|.\|. \f3esac\fP
A
.B case
command executes the
.I list
associated with the first
.I pattern
that matches
.IR word .
The form of the patterns is
the same as that used for
file-name generation (see
.I "File Name Generation"
below).
The
.B ;;
operator causes execution of
.B case
to terminate.
If
.B ;&
is used in place of
.B ;;
the next subsequent list, if any,  is executed.
.TP
\f3if\fP \f2list\^\fP \f3;then\fP \f2list\^\fP \*(OK \
\f3elif\fP \f2list\^\fP \f3;then\fP \f2list\^\fP \*(CK .\|.\|. \
\*(OK \f3;else\fP \f2list\^\fP \*(CK \f3;f\&i\fP
The
.I list
following \f3if\fP is executed and,
if it
returns a zero exit status, the
.I list
following
the first
.B then
is executed.
Otherwise, the
.I list
following \f3elif\fP
is executed and, if its value is zero,
the
.I list
following
the next
.B then
is executed.
Failing each successive
.B elif
.IR list\^ ,
the
.B else
.I list
is executed.
If the
.B if
.I list
has non-zero exit status
and there is no
.B else
.IR list ,
then the
.B if
command returns a zero exit status.
.TP
.PD 0
\f3while\fP \f2list\^\fP \f3;do\fP \f2list\^\fP \f3;done\fP
.TP
\f3until\fP \f2list\^\fP \f3;do\fP \f2list\^\fP \f3;done\fP
.PD
A
.B while
command repeatedly executes the
.B while
.I list
and, if the exit status of the last command in the list is zero, executes
the
.B do
.IR list ;
otherwise the loop terminates.
If no commands in the
.B do
.I list
are executed, then the
.B while
command returns a zero exit status;
.B until
may be used in place of
.B while
to negate
the loop termination test.
.TP
\f3((\fP\f2expression\^\fP\f3))\fP
.br
The
.I expression
is evaluated using the rules for arithmetic evaluation described below.
If the value of the arithmetic expression is non-zero, the exit
status is 0, otherwise the exit status is 1.
.TP
\f3(\fP\f2list\^\fP\f3)\fP
.br
Execute
.I list
in a separate environment.
Note, that if two adjacent open parentheses are
needed for nesting, a space must be inserted to avoid
evaluation as an arithmetic command as described above.
.TP
\f3{ \fP\f2list\^\fP\f3;}\fP
.br
.I list
is simply executed.
Note that unlike the metacharacters
.B (
and
.BR ) ,
.B {
and
.B }
are
.IR "reserved word" s
and must occur
at the beginning of a line or after a
.B ;
in order to be recognized.
.TP
\f3[[\fP\f2 expression \^\fP\f3]]\fP
.br
Evaluates
.I expression
and returns a zero exit status when
.I expression
is true.
See
.I "Conditional Expressions"
below, for a description of
.IR expression .
.TP
.PD 0
\f3function\fP \f2varname\^\fP \f3{\fP \f2list\^\fP \f3;}\fP
.TP
\f2varname\^\fP \f3() {\fP \f2list\^\fP \f3;}\fP
.PD
Define a function which is referenced by
.IR varname .
A function whose
.I varname
contains a
.B \s+2.\s-2
is called a discipline function and the portion
of the
.I varname
preceding the last
.B \s+2.\s-2
must refer to an existing variable. 
The body of the function is the
.I list
of commands between
.B {
and
.BR } .
A function defined with the \f3function\fP \f2varname\^\fP
syntax can also be used as an argument to the \f3.\fP
special built-in command to get the equivalent behavior
as if the \f2varname\^\fP\f3()\fP syntax were used to define it.
(See
.I Functions
below.)
.TP
\f3time\fP \*(OK \f2pipeline\^\fP \*(CK
.br
If \f2pipeline\^\fP is omitted the user and system time for
the current shell and completed child processes is printed
on standard error.
Otherwise,
.I pipeline
is executed and the elapsed time as well as
the user and system time are printed on standard error.
.PP
The following reserved words
are recognized as reserved only when they are the first word of a command
and are not quoted:
.PP
.if t .RS
.B
.if n if then else elif fi case esac for while until do done { } function select time [[ ]] !
.if t if   then   else   elif   fi   case   esac   for   while   until   do   done   {   }   function   select   time  [[  ]]   !
.if t .RE
.SS Variable Assignments.
One or more variable assignments can start a simple command
or can be arguments to the
.BR typeset ,
.BR export ,
or
.B readonly
special built-in commands.
The syntax for an \f2assignment\^\fP is of the form:
.TP
.PD 0
\f2varname\^\fP\f3=\fP\f2word\^\fP
.TP
\f2varname\^\fP\f3[\fP\f2word\^\fP\f3]\fP=\fP\f2word\^\fP
.PD
No space is permitted between \f2varname\^\fP and the \f3=\fP or
between \f3=\fP and \fIword\^\fP.
.TP
\f2varname\^\fP\f3=(\fP\f2assign_list\^\fP\f3)\fP
No space is permitted between \f2varname\^\fP and the \f3=\fP.
An \f2assign_list\^\fP can be one of the following:
.RS 15
.PD 0
.TP
\f2word\^\fP ...
Indexed array assignment.
.TP
\f3[\fP\f2word\^\fP\f3]=\fP\f2word\^\fP .\|.\|.
Associative array assignment.
.TP
\f2assignment\^\fP .\|.\|.
Nested variable assignment.
.TP
\f3typeset\fP \*(OK\f2options\fP\*(CK \f2assignment\^\fP .\|.\|.
Nested variable assignment.  Multiple assignments
can be specified by separating each of them with a \f3;\fP.
.PD
.RE
.SS Comments.
A word beginning with
.B #
causes that word and all the following characters up to a new-line
to be ignored.
.SS Aliasing.
The first word of each command is replaced by the text of an
.B alias
if an
.B alias
for this word has been defined.
An
.B alias
name consists of any number of characters excluding metacharacters,
quoting characters,
file expansion characters,
parameter expansion and command substitution
characters,
and
.BR = .
The replacement string can contain any
valid shell script
including the metacharacters listed above.
The first word of each command in the
replaced text,
other than
any that are in the process of being replaced,
will be tested for aliases.
If the last character of the alias value is a
.I blank
then the word following the alias will also be checked for alias
substitution.
Aliases can be used to redefine
built-in commands but cannot be used to redefine
the reserved words listed above.
Aliases can be created and listed with the
.B alias
command and can be removed with the
.B unalias
command.
.PP
.I Aliasing
is performed when
scripts are read,
not while they are executed.
Therefore,
for an alias to take effect,
the
.B
alias
definition command has to be executed before
the command which references the alias is read.
.PP
The following aliases
are compiled into the shell
but can be unset or redefined:
.RS 20
.PD 0
.TP
.B "autoload=\(fmtypeset \-fu\(fm"
.TP
.B "command=\(fmcommand  \(fm"
.TP
.B "fc=hist"
.TP
.B "float=\(fmtypeset \-E\(fm"
.TP
.B "functions=\(fmtypeset \-f\(fm"
.TP
.B "hash=\(fmalias \-t \-\^\-\(fm"
.TP
.B "history=\(fmhist \-l\(fm"
.TP
.B "integer=\(fmtypeset \-i\(fm"
.TP
.B "nameref=\(fmtypeset \-n\(fm"
.TP
.B "nohup=\(fmnohup  \(fm"
.TP
.B "r=\(fmhist \-s\(fm"
.TP
.B "redirect=\(fmcommand exec\(fm"
.TP
.B "stop=\(fmkill \-s \s-1STOP\s+1\(fm"
.TP
.B "suspend=\(fmkill \-s \s-1STOP\s+1 $$\(fm"
.TP
.B "times=\(fm{ { time;} 2>&1;}\(fm"
.TP
.B "type=\(fmwhence \-v\(fm"
.PD
.RE
.SS Tilde Substitution.
After alias substitution is performed, each word
is checked to see if it begins with an unquoted
.BR \(ap .
For tilde substitution,
.I word
also refers to the
.I word
portion of parameter expansion
(see
.I "Parameter Expansion"
below).
If it does, then the word up to a
.B /
is checked to see if it matches a user name in the
password database (often the
.B /etc/passwd
file).
If a match is found, the
.B \(ap
and the matched login name are replaced by the
login directory of the matched user.
If no match is found, the original text is left unchanged.
A
.B \(ap
by itself, or in front of a
.BR / ,
is replaced by
.SM
.BR $HOME .
A
.B \(ap
followed by a
.B +
or
.B \-
is replaced by the value of
.B
.SM $PWD
and
.B
.SM $OLDPWD
respectively.
.PP
In addition,
when expanding a
.IR "variable assignment" ,
.I tilde
substitution is attempted when
the value of the assignment
begins with a
.BR \(ap ,
and when a
.B \(ap
appears after a
.BR : .
The
.B :
also terminates a
.B \(ap
login name.
.if \nY=1 \{.PP 
On R&D UNIX Systems with RFS, an additional capability,
.BR \(aphost!user ,
has been added to 
.IR ksh .
See
.IR logdir (1)
for a complete description of the capability.\}
.SS Command Substitution.
The standard output from a command enclosed in
parentheses preceded by a dollar sign (
.B $(\|)
)
or a pair of grave accents (\^\f3\*`\^\*`\fP\^)
may be used as part or all
of a word;
trailing new-lines are removed.
In the second (obsolete) form, the string between the quotes is processed
for special quoting characters before the command is executed (see
.I Quoting
below).
The command substitution
\^\f3$(\^cat file\^)\fP\^
can be replaced by the equivalent but faster
\^\f3$(\^<file\^)\fP\^.
.SS Arithmetic Substitution.
An arithmetic expression enclosed in double
parentheses preceded by a dollar sign (
.B $((\|))
)
is replaced by the value of the arithmetic expression
within the double parentheses.
.SS Process Substitution.
This feature is only available on
versions of the UNIX operating system that support the
.B /dev/fd
directory for naming open files.
Each command argument of the form
\f3<(\fP\f2list\^\fP\f3)\fP
or
\f3>(\fP\f2list\^\fP\f3)\fP
will run process
.I list
asynchronously connected to some file in
.BR /dev/fd .
The name of this file will become the argument to the command.
If the form with
.B >
is selected then writing on this file will provide input for
.IR list .
If
.B <
is used,
then the file passed as an argument will contain the output of the
.I list
process.
For example,
.PP
.RS
\f3paste <(cut \-f1\fP \f2file1\fP\f3) <(cut \-f3\fP \f2file2\f3) | tee >(\fP\f2process1\fP\f3) >(\fP\f2process2\fP\f3)\fP
.RE
.PP
.I cuts
fields 1 and 3 from
the files
.I file1
and
.I file2
respectively,
.I pastes
the results together, and
sends it
to the processes
.I process1
and
.IR process2 ,
as well as putting it onto the standard output.
Note that the file, which is passed as an argument to the command,
is a UNIX
.IR pipe (2)
so programs that expect to
.IR lseek (2)
on the file will not work.
.SS Parameter Expansion.
A
.I parameter
is a
.IR variable ,
one or more digits,
or any of the characters
.BR \(** ,
.BR @ ,
.BR # ,
.BR ? ,
.BR \- ,
.BR $ ,
and
.BR !\^ .
A
.I variable
is denoted by a \f2vname\fP.
To create a variable whose
.I vname
contains a \f3\s+2.\s-2\fP,
a variable whose
.I vname
consists of everything before the last \f3\s+2.\s-2\fP must already exist.
A
.I variable
has a
.I value
and zero or more
.IR attributes .
.I Variables
can be assigned
.I values
and
.I attributes
by using the
.B typeset
special built-in command.
The attributes supported by the shell are described
later with the
.B typeset
special built-in command.
Exported variables pass values and attributes to
the environment.
.PP
The shell supports both indexed and associative arrays.
An element of an array variable is referenced by a
.IR subscript .
A
.I subscript
for an indexed array is denoted by
an
.I arithmetic expression
(see
.I "Arithmetic Evaluation"
below)
between a
.B [
and a
.BR ] .
To assign values to an indexed array, use
\f3set \-A\fP \f2vname\fP  \f2value\fP .\|.\|. .
The value of all
subscripts must be in the
range of
0 through 4095.
Indexed arrays need not be declared.
Any reference to a variable
with a valid subscript is
legal and an array will be created if necessary.
.PP
An associative array is created with the
.B \-A
option to
.BR typeset.
A
.I subscript
for an associative array is denoted by
a string enclosed between
.B [
and
.BR ] .
.PP
Referencing any array without a subscript
is equivalent to referencing the array with subscript 0.
.PP
The
.I value
of a
.I variable
may be assigned by writing:
.PP
.RS
.IB vname = value\^\|
\*(OK
.IB vname = value
\*(CK .\|.\|.
.RE
.PP
.PD 0
or
.PP
.RS
.IB vname [ subscript ]= value\^\|
\*(OK
.IB vname [ subscript ]= value
\*(CK .\|.\|.
.sp .5
.RE
Note that no space is allowed before or after the
.BR = .
.sp .5
.PP
.PD 0
A
.I nameref
is a variable that is a reference to another variable.
A nameref is created with the
.B \-n
attribute of
.BR typeset .
The value of the variable at the time of the
.B typeset
command becomes the variable that will be referenced whenever
the nameref variable is used.
The name of a nameref cannot contain a \fB\s+2.\s-2\fP.
When a variable or function name contains a \fB\s+2.\s-2\fP, and the portion
of the name up to the first \fB\s+2.\s-2\fP matches the
name of a nameref, the variable referred to is obtained by
replacing the nameref portion with the name of the variable
referenced by the nameref.
A nameref provides a convenient way to refer to the variable
inside a function whose name is passed as an argument to a function.
For example, if the name of a variable is passed as the first
argument to a function, the command
.PP
.RS
\fBtypeset \-n var=$1\fR
.RE
.PP
inside the function causes references and assignments to
.B var
to be references and assignments to the variable whose
name has been passed to the function.
.sp .5
.PP
If either of the floating point attributes,
.BR \-E ,
or
.BR \-F ,
or the integer attribute,
.BR \-i ,
is set for
.IR vname ,
then the
.I value
is subject to arithmetic evaluation as described below.
.sp .5
.PP
Positional parameters,
parameters denoted by a number,
may be assigned values with the
.B set
special built-in command.
Parameter
.B $0
is set from argument zero when the shell
is invoked.
.sp .5
.PP
The character
.B $
is used to introduce substitutable
.IR parameters .
.TP
\f3${\fP\f2parameter\^\fP\f3}\fP
The shell
reads all the characters from
.B ${
to the matching
.B }
as part of the same word even if it contains
braces or metacharacters.
The value, if any, of the parameter is substituted.
The braces are required when
.I parameter
is followed by a letter, digit, or underscore
that is not to be interpreted as part of its name,
when the variable name contains a \fB\s+2.\s-2\fP,
or when a variable is subscripted.
If
.I parameter
is one or more digits then it is a positional parameter.
A positional parameter of more than one digit must be
enclosed in braces.
If
.I parameter
is
.B \(**
or
.BR @ ,
then all the positional
parameters, starting with
.BR $1 ,
are substituted
(separated by a field separator character).
If an array
.I vname
with subscript
.B \(**
or
.B @
is used,
then the value
for each of the
elements
is substituted,
separated by
the first character of
the value of
.SM
.BR IFS .
.TP
\f3${#\fP\f2parameter\^\fP\f3}\fP
If
.I parameter
is
.B \(**
or
.BR @ ,
the number of positional parameters is substituted.
Otherwise, the length of the value of the
.I parameter
is substituted.
.TP
.PD 0
\f3${#\fP\f2vname\fP\f3[*]}\fP
.TP
.PD
\f3${#\fP\f2vname\fP\f3[@]}\fP
The number of elements in the array
.I vname
is substituted.
.TP
\f3${!\fP\f2vname\^\fP\f3}\fP
Expands to the name of the variable referred to by
.IR vname .
This will be
.I vname
except when
.I vname
is a name reference.
.TP
\f3${!\fP\f2vname\^\fP\f3[\f2subscript\^\f3]}\fP
Expands to name of the subscript unless
.I subscript
is
.B *
or
.BR @ .
When
.I subscript
is
.BR * ,
the list of array subscripts for \f2vname\^\fP
is generated.
For a variable that is not an array, the value is 0 if the variable
is set.  Otherwise it is null.
When
.I subscript
is
.BR @ ,
same as above, except that when used in double quotes,
each array subscript yields a separate
argument.
.TP
\f3${!\fP\f2prefix\^\fP\f3*}\fP
Expands to the names of the variables whose names begin with
.IR prefix .
.TP
\f3${\fP\f2parameter\^\fP\f3:\-\fP\f2word\^\fP\f3}\fP
If
.I parameter
is set and is non-null then substitute its value;
otherwise substitute
.IR word .
.TP
\f3${\fP\f2parameter\^\fP\f3:=\fP\f2word\^\fP\f3}\fP
If
.I parameter
is not set or is null then set it to
.IR word ;
the value of the parameter is then substituted.
Positional parameters may not be assigned to
in this way.
.TP
\f3${\fP\f2parameter\^\fP\f3:?\fP\f2word\^\fP\f3}\fP
If
.I parameter
is set and is non-null then substitute its value;
otherwise, print
.I word
and exit from the shell (if not interactive).
If
.I word
is omitted then a standard message is printed.
.TP
\f3${\fP\f2parameter\^\fP\f3:+\fP\f2word\^\fP\f3}\fP
If
.I parameter
is set and is non-null then substitute
.IR word ;
otherwise substitute nothing.
.TP
.PD 0
\f3${\fP\f2parameter\^\fP\f3:\fP\f2offset\^\fP\f3:\fP\f2length\^\fP\f3}\fP
.TP
\f3${\fP\f2parameter\^\fP\f3:\fP\f2offset\^\fP\f3}\fP
Expands to the portion of the value of
.I parameter
starting at the character (counting from
.BR 0\^ )
determined by expanding
.I offset
as an arithmetic expression and consisting of the
number of characters determined by the arithmetic expression
defined by
.IR length.
In the second form, the remainder of the value is used. 
If
.I parameter
is
.B \(**
or
.BR @ ,
or is an array name indexed by
.B \(**
or
.BR @ ,
then
.I offset
and
.I length
refer to the array index and number
of elements respectively.
.TP
.PD 0
\f3${\fP\f2parameter\^\fP\f3#\fP\f2pattern\^\fP\f3}\fP
.TP
\f3${\fP\f2parameter\^\fP\f3##\fP\f2pattern\^\fP\f3}\fP
.PD
If
the shell
.I pattern
matches the beginning of the value of
.IR parameter ,
then the value of
this expansion is the value of the
.I parameter
with the matched portion deleted;
otherwise the value of this
.I parameter
is substituted.
In the first form the smallest matching pattern is deleted and in the
second form the largest matching pattern is deleted.
When
.I parameter
is
.BR @ ,
.BR * ,
or an array variable with subscript
.B @
or
.BR * ,
the substring operation is applied to each element in turn.
.TP
.PD 0
\f3${\fP\f2parameter\^\fP\f3%\fP\f2pattern\^\fP\f3}\fP
.TP
\f3${\fP\f2parameter\^\fP\f3%%\fP\f2pattern\^\fP\f3}\fP
.PD
If
the shell
.I pattern
matches the end of the value of
.IR parameter ,
then the value of
this expansion is the value of the
.I parameter
with the matched part deleted;
otherwise substitute the value of
.IR parameter .
In the first form the smallest matching pattern is deleted and in the
second form the largest matching pattern is deleted.
When
.I parameter
is
.BR @ ,
.BR * ,
or an array variable with subscript
.B @
or
.BR * ,
the substring operation is applied to each element in turn.
.TP
.PD 0
\f3${\fP\f2parameter\^\fP\f3/\fP\f2pattern\^\fP\f3/\f2string\^\fP\f3}\fP
.TP
\f3${\fP\f2parameter\^\fP\f3//\fP\f2pattern\^\fP\f3/\f2string\^\fP\f3}\fP
.TP
\f3${\fP\f2parameter\^\fP\f3/#\fP\f2pattern\^\fP\f3/\f2string\^\fP\f3}\fP
.TP
\f3${\fP\f2parameter\^\fP\f3/%\fP\f2pattern\^\fP\f3/\f2string\^\fP\f3}\fP
.PD
Expands
.I parameter
and replaces the longest match of
.I pattern
with the given
.IR string.
Each occurrence of \f3\e\fP\f2n\^\fP in
.I string
is replaced by the portion of \f2parameter\^\fP
that matches the \f2n\^\fP-th sub-pattern.
In the first form,
only the first occurrence of
.I pattern
is replaced.
In the second form,
each match for
.I pattern
is replaced by the given
.IR string.
The third form restricts the pattern match to the beginning of the string
while the fourth form restricts the pattern match to the end of
the string.
When 
.I string
is null, the
.I pattern
will be deleted and the
.B /
in front of
.I string
may be omitted.
When
.I parameter
is
.BR @ ,
.BR * ,
or an array variable with subscript
.B @
or
.BR * ,
the substitution operation is applied to each element in turn.
.PP
In the above,
.I word
is not evaluated unless it is
to be used as the substituted string,
so that, in the following example,
.B pwd
is executed only if
.B d
is not set or is null:
.PP
.RS
print \|${d:\-\^$(\^pwd\^)\^}
.RE
.PP
If the colon (
.B : )
is omitted from the above expressions,
then the shell only checks whether
.I parameter
is set or not.
.PP
The following
parameters
are automatically set by the shell:
.RS
.PD 0
.TP
.B #
The number of positional parameters in decimal.
.TP
.B \-
Options supplied to the shell on invocation or by
the
.B set
command.
.TP
.B ?
The decimal value returned by the last executed command.
.TP
.B $
The process number of this shell.
.TP
.B _
Initially, the value of
.B _
is an absolute pathname of the shell or script being executed
as passed in the
.IR environment .
Subsequently it is assigned the last argument of the previous command.
This parameter is not set for commands which are asynchronous.
This parameter is also used to hold the name of the matching
.B
.SM MAIL
file when checking for mail.
.TP
.B !
The process number of the last background command invoked.
.TP
.B .sh.edchar
This variable contains the value of the keyboard character
(or sequence of characters if the first character is an ESC, ascii
.BR 033\^ )
that has
been entered when processing a
.B
.SM KEYBD
trap
(see
.I "Key Bindings"
below).
If the value is changed as part of the trap action, then the new
value replaces the key (or key sequence) that caused the trap.
.TP
.B .sh.edcol
The character position of the cursor at the time of the most recent
.B
.SM KEYBD
trap.
.TP
.B .sh.edmode
The value is set to ESC when processing a
.B
.SM KEYBD
trap while in
.B vi
insert mode.  (See
.I "Vi Editing Mode"
below.)
Otherwise,
.B .sh.edmode
is null when processing a
.B
.SM KEYBD
trap.
.TP
.B .sh.edtext
The characters in the input buffer at the time of the most recent
.B
.SM KEYBD
trap.
The value is null when not processing a
.B
.SM KEYBD
trap.
.TP
.B .sh.name
Set to the name of the variable at the time that a
discipline function is invoked.
.TP
.B .sh.subscript
Set to the name subscript of the variable at the time that a
discipline function is invoked.
.TP
.B .sh.value
Set to the value of the variable at the time that the
.B set
discipline function is invoked.
.TP
.B .sh.version
Set to a value that identifies the version of this shell.
.TP
.B
.SM LINENO
The current line number within the script or
function being executed.
.TP
.B
.SM OLDPWD
The previous working directory set by the
.B cd
command.
.TP
.B
.SM OPTARG
The value of the last option argument processed by the
.B getopts
built-in command.
.TP
.B
.SM OPTIND
The index of the last option argument processed by the
.B getopts
built-in command.
.TP
.B
.SM PPID
The process number of the parent of the shell.
.TP
.B
.SM PWD
The present working directory set by the
.B cd
command.
.TP
.B
.SM RANDOM
Each time this variable is referenced, a random integer,
uniformly distributed between 0 and 32767, is generated.
The sequence of random numbers can be initialized by assigning
a numeric value to
.SM
.BR RANDOM .
.TP
.B
.SM REPLY
This variable is set by the
.B select
statement and by
the
.B read
built-in command when no arguments are supplied.
.TP
.B
.SM SECONDS
Each time this variable is referenced, the number of
seconds since shell invocation is returned.
If this variable is
assigned a value, then the value returned upon reference will
be the value that was assigned plus the number of seconds since the assignment.
.PD
.RE
.PP
The following
variables
are used by the shell:
.RS
.PD 0
.TP
.B
.SM CDPATH
The search path for the
.B cd
command.
.TP
.B
.SM COLUMNS
If this variable is set,
the value is used to define the width of the edit window
for the shell edit modes and for printing
.B select
lists.
.TP
.B
.SM EDITOR
If the value of this variable ends in
.IR emacs ,
.IR gmacs ,
or
.I vi
and the
.B
.SM VISUAL
variable is not set,
then the corresponding option
(see special built-in command
.B set
below)
will be turned on.
.TP
.SM
.B ENV
If this variable is set, then
parameter expansion, command substitution, and arithmetic substitution
are performed on
the value to generate
the pathname of the script that will be
executed when the shell
is invoked
(see
.I Invocation
below).
This file is typically used for
.B alias
and
.B function
definitions.
.TP
.B
.SM FCEDIT
Obsolete name for
the default editor name for the
.B hist
command.
.B
.SM FCEDIT
is not used when
.B
.SM HISTEDIT
is set.
.TP
.SM
.B FIGNORE
A pattern that defines the set of filenames that will be
ignored when performing filename matching.
.TP
.SM
.B FPATH
The search path for function definitions.
This path is searched for a file with the same name
as the function or command when a function with the
.B \-u
attribute is referenced and when a command is not found.
If an executable file with the name of that command is found,
then it is read and executed
in the current environment.
.TP
.B
.SM HISTCMD
Number of the current command in the history file.
.TP
.B
.SM HISTEDIT
Name for
the default editor name for the
.B hist
command.
.TP
.SM
.B HISTFILE
If this variable is set when the shell is invoked, then
the value is the pathname of the file that will be
used to store the command history (see
.I "Command Re-entry"
below).
.TP
.SM
.B HISTSIZE
If this variable is set when the shell is invoked, then
the number of previously entered commands that
are accessible by this shell
will be greater than or equal to this number.
The default is 128.
.TP
.B
.SM HOME
The default argument (home directory) for the
.B cd
command.
.TP
.SM
.B IFS
Internal field separators,
normally
.BR space ,
.BR tab ,
and
.B new-line
that are used to separate the results of
command substitution or parameter expansion
and to separate fields with the built-in command
.BR read .
The first character of the
.SM
.B IFS
variable is used to separate arguments for the
.B
"$\(**"
substitution (see
.I Quoting
below).
Each single occurrence of
an
.SM
.B IFS
character in the string to be split,
that is not in the \f2isspace\^\fP character class, and any
adjacent characters in
.SM
.B IFS
that are in the \f2isspace\^\fP character class, delimit a field.
One or more
characters in
.SM
.B IFS
that belong to the \f2isspace\^\fP character class,
delimit a field.
In addition, if the same \f2isspace\^\fP character appears
consecutively inside
.SM
.BR IFS ,
this character is treated as if it were not in the \f2isspace\^\fP
class, so that if
.SM
.BR IFS
consists of two
.B tab
characters,
then two adjacent
.B tab
characters delimit a null field.
.TP
.B
.SM LANG
This variable determines the locale category for any
category not specifically selected with a variable
starting with
.B
.SM LC_
or
.SM
.BR LANG .
.TP
.B
.SM LC_ALL
This variable overrides the value of the
.B
.SM LANG
variable and any other
.B
.SM LC_
variable.
.TP
.B
.SM LC_COLLATE
This variable determines the locale category for character
collation information.
.TP
.B
.SM LC_CTYPE
This variable determines the locale category for character
handling functions.
It determines the character classes for pattern matching (see
.I "File Name Generation"
below).
.TP
.B
.SM LC_NUMERIC
This variable determines the locale category for the
decimal point character.
.TP
.B
.SM LINES
If this variable is set,
the value is used to determine the column length for printing
.B select
lists.
Select lists will print vertically until about two-thirds of
.B
.SM LINES
lines are filled.
.TP
.B
.SM MAIL
If this variable is set to the name of a mail file
.I and
the
.B
.SM MAILPATH
variable is not set,
then the shell informs the user of arrival of mail
in the specified file.
.TP
.B
.SM MAILCHECK
This variable specifies how often (in seconds) the
shell will check for changes in the modification time
of any of the files specified by the
.B
.SM MAILPATH
or
.B
.SM MAIL
variables.
The default value is 600 seconds.
When the time has elapsed
the shell will check before issuing the next prompt.
.TP
.B
.SM MAILPATH
A colon (
.B :
)
separated list of file names.
If this variable is set,
then the shell informs the user of
any modifications to the specified files
that have occurred within the last
.B
.SM MAILCHECK
seconds.
Each file name can be followed by a
.B ?
and a message that will be printed.
The message will undergo parameter expansion, command substitution,
and arithmetic substitution
with the variable
.B $_
defined as the name of the file that has changed.
The default message is
.I you have mail in $_\^.
.TP
.B
.SM PATH
The search path for commands (see
.I Execution
below).
The user may not change
.B \s-1PATH\s+1
if executing under
.if \nZ=0 .B rsh
.if \nZ=1 .B rksh
(except in
.BR .profile\^).
.TP
.SM
.B PS1
The value of this variable is expanded for parameter
expansion, command substitution, and arithmetic substitution to define the
primary prompt string which by default is
.RB `` "$\|\|\|" ''.
The character
.B !
in the primary prompt string is replaced by the
.I command
number (see
.I "Command Re-entry"
below).
Two successive occurrences of
.B !
will produce a single
.B !
when the prompt string is printed.
.TP
.SM
.B PS2
Secondary prompt string, by default
.RB `` "> \|" ''.
.TP
.SM
.B PS3
Selection prompt string
used within a
.B select
loop, by default
.RB `` "#? \|" ''.
.TP
.SM
.B PS4
The value of this variable is expanded for parameter evaluation,
command substitution, and arithmetic substitution
and precedes each line of an execution trace.
By default,
.SM
.B PS4
is
.RB `` "+ \|" ''.
In addition
when
.SM
.B PS4
is unset,
the execution trace prompt is also
.RB `` "+ \|" ''.
.TP
.SM
.B SHELL
The pathname of the
.I shell
is kept in the environment.
At invocation, if the basename of this variable is
.BR rsh ,
.BR rksh ,
or
.BR krsh ,
then the shell becomes restricted.
.TP
.B
.SM TMOUT
If set to a value greater than zero,
.B
.SM TMOUT
will be the default timeout value for the
.B read
built-in command.
The
.B select
compound command terminates after
.B
.SM TMOUT
seconds when input is from a terminal.
Otherwise,
the shell will terminate if a line is not entered within
the prescribed number of seconds while reading from a terminal.
(Note that the shell can be compiled with a maximum bound
for this value which cannot be exceeded.)
.TP
.B
.SM VISUAL
If the value of this variable ends in
.IR emacs ,
.IR gmacs ,
or
.I vi
then the corresponding option
(see Special Command
.B set
below)
will be turned on.
The value of
.B
.SM VISUAL
overrides the value of
.B
.SM EDITOR.
.PD
.RE
.PP
The shell gives default values to
\f3\s-1PATH\s+1\fP, \f3\s-1PS1\s+1\fP, \f3\s-1PS2\s+1\fP,
\f3\s-1PS3\s+1\fP, \f3\s-1PS4\s+1\fP, \f3\s-1MAILCHECK\s+1\fP, \f3\s-1FCEDIT\s+1\fP,
\f3\s-1TMOUT\s+1\fP and \f3\s-1IFS\s+1\fP,
while
.SM
.BR HOME ,
.SM
.BR SHELL ,
.SM
.BR ENV ,
and
.SM
.B MAIL
are
not set at all by the shell (although
.SM
.B HOME
.I is
set by
.IR login (1)).
On some systems
.SM
.B MAIL
and
.SM
.B SHELL
are also
set by
.IR login (1).
.SS Field Splitting.
After parameter expansion and command substitution,
the results of substitutions are scanned for the field separator
characters (those found in
.SM
.B IFS\^\c
)
and split into distinct fields where such characters are found.
Explicit null fields (\^\f3"\^"\fP or \f3\(fm\^\(fm\fP\^) are retained.
Implicit null fields
(those resulting from
.I parameters
that have no values or command substitutions with no output) are removed.
.SS File Name Generation.
Following splitting, each field is scanned for the characters
.BR \(** ,
.BR ? ,
.BR ( ,
and
.B \*(OK
unless the
.B \-f
option has been set.
If one of these characters appears,
then the word is regarded as a
.IR pattern .
Each file name component that contains any pattern character
is replaced with a lexicographically sorted set of names
that matches the pattern
from
that directory.
If no file name is found that matches the pattern, then
that component of the filename is left unchanged.
If
.SM
.B FIGNORE
is set,
then each file name component
that matches the pattern defined by the value of 
.SM
.B FIGNORE
is ignored when generating the matching filenames.
The names
.B .
and
.B ..
are also ignored.
If
.SM
.B FIGNORE
is not set,
the character
.B .
at the start of each file name component
will be ignored unless the first character of the pattern
corresponding to this component is the character
.BR .
itself.
Note, that for other
uses of pattern matching the
.B /
and
.B .
are not treated specially.
.PP
.PD 0
.RS
.TP
.B \(**
Matches any string, including the null string.
.TP
.B ?
Matches any single character.
.TP
.BR \*(OK \^.\|.\|.\^ \*(CK
Matches any one of the enclosed characters.
A pair of characters separated by
.B \-
matches any
character lexically between the pair, inclusive.
If the first character following the opening
.B \*(OK
is a
.B !
then any character not enclosed is matched.
A
.B \-
can be included in the character set by putting it as the
first or last character.
.br
Within
.B \*(OK
and
.BR \*(CK\^ ,
character classes can be specified with the syntax
\f3[:\fP\f2class\fP\f3:]\fP
where class is one of the following classes defined in the ANSI-C standard:
.PP
.if t .RS
.B
.if n alnum alpha blank cntrl digit graph lower print punct space upper xdigit
.if t alnum   alpha   blank   cntrl   digit   graph   lower   print   punct   space   upper   xdigit
.br
Within
.B \*(OK
and
.BR \*(CK\^ ,
an equivalence class can be specified with the syntax
\f3[=\fP\f2c\fP\f3=]\fP
which matches all characters with the same primary
collation weight (as defined by the current locale) as
the character \f2c\fP.
.br
Within
.B \*(OK
and
.BR \*(CK\^ ,
\f3[.\fP\f2symbol\fP\f3.]\fP
matches the collating symbol \f2symbol\fP.
.if t .RE
.PD
.RE
A
.I pattern-list
is a list of one or more patterns separated from each other
with a
.B &
or
.BR \(bv .
A
.B &
signifies that all patterns must be matched whereas
.BR \(bv
requires that only one pattern be matched.
Composite patterns can be formed with one or more of the following sub-patterns:
.PD 0
.RS
.TP
\f3?(\fP\f2pattern-list\^\fP\f3)\fP
Optionally matches any one of the given patterns.
.TP
\f3*(\fP\f2pattern-list\^\fP\f3)\fP
Matches zero or more occurrences of the given patterns.
.TP
\f3+(\fP\f2pattern-list\^\fP\f3)\fP
Matches one or more occurrences of the given patterns.
.TP
\f3\&@\&(\fP\f2pattern-list\^\fP\f3)\fP
Matches exactly one of the given patterns.
.br
.TP
\f3!(\fP\f2pattern-list\^\fP\f3)\fP
Matches anything except one of the given patterns.
.PD
.RE
Each sub-pattern in a composite pattern is numbered,
starting at 1, by the location of the \f3(\fP within
the pattern.
The sequence \f3\e\fP\f2n\^\fP, where \f2n\^\fP 
is a single digit and \f3\e\fP\f2n\^\fP comes after
the \f2n\fP-th. sub-pattern,
matches the same string as the sub-pattern itself.
.SS Quoting.
Each of the
.I metacharacters
listed earlier (see
.I Definitions
above)
has a special meaning to the shell
and causes termination of a word unless quoted.
A character may be
.I quoted
(i.e., made to stand for itself)
by preceding
it with a
.BR \e .
The pair
.B \enew-line
is removed.
All characters enclosed between a pair of single quote marks
(\^\f3\(fm\^\(fm\fP\^)
that is not preceded by a
.B $
are quoted.
A single quote cannot appear within the single quotes.
A single quoted string preceded by an unquoted
.B $
is processed as an ANSI-C string
except that
.B \e0
within the string causes the remainder of the
string to be ignored and
.B \eE
is equivalent to the escape character
(ascii
.BR 033 ).
Inside double quote marks
(\f3"\^"\fP),
parameter and command substitution occur and
.B \e
quotes the characters
.BR \e ,
.BR \*` ,
\f3"\fP,
and
.BR $ .
A
.B $
in front of a double quoted string will be ignored
in the "C" or "POSIX" locale, and may cause
the string to be replaced by a locale specific string otherwise.
The meaning of
.B "$\(**"
and
.B "$@"
is identical when not quoted or when used as a variable assignment value
or as a file name.
However, when used as a command argument,
.B
"$\(**"
is equivalent to
\f3"$1\fP\f2d\fP\f3\|$2\fP\f2d\fP\|.\|.\|.\f3"\fP,
where
.I d
is the first character of the
.SM
.B IFS
variable, whereas
.B
"$@"
is equivalent to
.B
"$1"\|
.B
"$2"\|
\&.\|.\|.\^.
Inside grave quote marks
(\f3\*`\^\*`\fP),
.B \e
quotes the characters
.BR \e ,
.BR \*` ,
and
.BR $ .
If the grave quotes occur within double quotes, then
.B \e
also quotes the character
\f3"\fP.
.PP
The special meaning of reserved words or aliases can be removed by quoting any
character of the reserved word.
The recognition of function names or built-in command names listed below
cannot be altered by quoting them.
.SS Arithmetic Evaluation.
The shell performs arithmetic evaluation for
arithmetic substitution, to evaluate an arithmetic command,
to evaluate an indexed array subscript, 
and to evaluate arguments to
the built-in commands
.B shift
and
.BR let .
Evaluations are performed using
double precision floating point
arithmetic.
Floating point constants follow the ANSI-C programming language
conventions.
Integer constants are of the form
\*(OK\f2base\fP\f3#\^\fP\*(CK\f2n\^\fP
where
.I base
is a decimal number between two and sixty-four
representing the arithmetic base
and
.I n
is a number in that base.
The digits above 9 are represented
by the lower case letters, the upper case letters,
.BR @ ,
and
.B _
respectively.
For bases less than or equal to 36, upper and lower case
characters can be used interchangeably.
If
.I base
is omitted,
then base 10 is used.
.PP
An arithmetic expression uses the same syntax, precedence, and
associativity of
expression as the C language.
All the C language operators
that apply to floating point quantities can be used.
In addition, when the value of an arithmetic variable
or sub-expression can be represented as a long integer,
all C language integer arithmetic operations can be performed. 
Variables can be referenced by name within an arithmetic expression
without using the parameter expansion syntax.
When a variable is referenced, its value is evaluated as
an arithmetic expression.
.PP
The following math library functions can be used with an arithmetic
expression:
.PP
.if t .RS
.B
.if n abs acos asin atan cos cosh exp int log sin sinh sqrt tan tanh
.if t abs   acos   asin   atan   cos   cosh   exp   int   log   sin   sinh   sqrt   tan   tanh
.if t .RE
.PP
An internal representation of a
.I variable
as a double precision floating point can be specified with the
\f3\-E\fP \*(OK\f2n\^\fP\*(CK
or
\f3\-F\fP \*(OK\f2n\^\fP\*(CK
option of the
.B typeset
special built-in command.
The
.B \-E
option causes the expansion of the value to be represented using
scientific notation when it is expanded.
The optional option argument
.I n
defines the number of significant figures.
The
.B \-F
option causes the expansion to be represented as a floating decimal number
when it is expanded.
The optional option argument
.I n
defines the number of places after the decimal point in this case.
.PP
An internal integer representation of a
.I variable
can be specified with the
\f3\-i\fP \*(OK\f2n\^\fP\*(CK
option of the
.B typeset
special built-in command.
The optional option argument
.I n
specifies an arithmetic base to be used when expanding the variable.
If you do not specify an arithmetic base,
the first assignment to the
variable determines the arithmetic base.
.PP
Arithmetic evaluation is performed on the value of each
assignment to a variable with the
.BR \-E ,
.BR \-F ,
or
.B \-i
attribute.
Assigning a floating point number to a
variable whose type is an integer causes the fractional
part to be truncated.
.PP
.SS Prompting.
When used interactively,
the shell prompts with the value of
.SM
.B PS1
after expanding it for parameter expansion, command substitution, and
arithmetic substitution,
before reading a command.
In addition, each single
.B !
in the prompt is replaced by the command number.
A
.B !!
is required to place
.B !
in the prompt.
If at any time a new-line is typed and further input is needed
to complete a command, then the secondary prompt
(i.e., the value of
.BR \s-1PS2\s+1 )
is issued.
.SS Conditional Expressions.
A
.I "conditional expression"
is used with the
.B [[
compound command to test attributes of files and to compare
strings.
Field splitting and file name generation are
not performed on the words between
.B [[
and
.BR ]] .
Each expression can be constructed from one or more
of the following unary or binary expressions:
.PD 0
.TP
\f2string\fP
True, if
.I string
is not null.
.TP
\f3\-a\fP \f2file\fP
Same as \f3\-e\fP below.
This is obsolete.
.TP
\f3\-b\fP \f2file\fP
True, if
.I file
exists and is a block special file.
.TP
\f3\-c\fP \f2file\fP
True, if
.I file
exists and is a character special file.
.TP
\f3\-d\fP \f2file\fP
True, if
.I file
exists and is a directory.
.TP
\f3\-e\fP \f2file\fP
True, if
.I file
exists.
.TP
\f3\-f\fP \f2file\fP
True, if
.I file
exists and is an ordinary file.
.TP
\f3\-g\fP \f2file\fP
True, if
.I file
exists and it has its setgid bit set.
.TP
\f3\-k\fP \f2file\fP
True, if
.I file
exists and it has its sticky bit set.
.TP
\f3\-n\fP \f2string\fP
True, if length of
.I string
is non-zero.
.TP
\f3\-o\fP \f2option\fP
True, if option named
.I option
is on.
.TP
\f3\-p\fP \f2file\fP
True, if
.I file
exists and is a fifo special file or a pipe.
.TP
\f3\-r\fP \f2file\fP
True, if
.I file
exists and is readable by current process.
.TP
\f3\-s\fP \f2file\fP
True, if
.I file
exists and has size greater than zero.
.TP
\f3\-t\fP \f2fildes\fP
True, if file descriptor number
.I fildes
is open and associated with a terminal device.
.TP
\f3\-u\fP \f2file\fP
True, if
.I file
exists and it has its setuid bit set.
.TP
\f3\-w\fP \f2file\fP
True, if
.I file
exists and is writable by current process.
.TP
\f3\-x\fP \f2file\fP
True, if
.I file
exists and is executable by current process.
If
.I file
exists and is a directory, then true if the current process
has permission to search in the directory.
.TP
\f3\-z\fP \f2string\fP
True, if length of
.I string
is zero.
.TP
\f3\-L\fP \f2file\fP
True, if
.I file
exists and is a symbolic link.
.TP
\f3\-O\fP \f2file\fP
True, if
.I file
exists and is owned by the effective user id of this process.
.TP
\f3\-G\fP \f2file\fP
True, if
.I file
exists and its group matches the effective group id of this process.
.TP
\f3\-S\fP \f2file\fP
True, if
.I file
exists and is a socket.
.TP
\f2file1\fP \f3\-nt\fP \f2file2\fP
True, if
.I file1
exists and
.I file2
does not, or
.I file1
is newer than
.IR file2 .
.TP
\f2file1\fP \f3\-ot\fP \f2file2\fP
True, if
.I file2
exists and
.I file1
does not, or
.I file1
is older than
.IR file2 .
.TP
\f2file1\fP \f3\-ef\fP \f2file2\fP
True, if
.I file1
and 
.I file2
exist and refer to the same file.
.TP
\f2string\fP \f3==\fP \f2pattern\fP
True, if
.I string
matches
.IR pattern .
Any part of
.I pattern
can be quoted to cause it to be matched as a string.
.TP
\f2string\fP \f3=\fP \f2pattern\fP
Same as \f3==\fP above, but is obsolete.
.TP
\f2string\fP \f3!=\fP \f2pattern\fP
True, if
.I string
does not match
.IR pattern .
.TP
\f2string1\fP \f3<\fP \f2string2\fP
True, if
.I string1
comes before
.I string2
based on ASCII value of their characters.
.TP
\f2string1\fP \f3>\fP \f2string2\fP
True, if
.I string1
comes after
.I string2
based on ASCII value of their characters.
.PP
The following obsolete arithmetic comparisons are also permitted:
.PD 0
.TP
\f2exp1\fP \f3\-eq\fP \f2exp2\fP
True, if
.I exp1
is equal to
.IR exp2 .
.TP
\f2exp1\fP \f3\-ne\fP \f2exp2\fP
True, if
.I exp1
is not equal to
.IR exp2 .
.TP
\f2exp1\fP \f3\-lt\fP \f2exp2\fP
True, if
.I exp1
is less than
.IR exp2 .
.TP
\f2exp1\fP \f3\-gt\fP \f2exp2\fP
True, if
.I exp1
is greater than
.IR exp2 .
.TP
\f2exp1\fP \f3\-le\fP \f2exp2\fP
True, if
.I exp1
is less than or equal to
.IR exp2 .
.TP
\f2exp1\fP \f3\-ge\fP \f2exp2\fP
True, if
.I exp1
is greater than or equal to
.IR exp2 .
.PD
.PP
In each of the above expressions, if
.I file
is of the form
\f3/dev/fd/\fP\f2n\fP,
where
.I n
is an integer,
then the test is applied to the open file whose
descriptor number is
.IR n .
.PP
A compound expression can be constructed from these primitives by
using any of the following, listed in decreasing order of precedence.
.PD 0
.TP
\f3(\fP\f2expression\fP\f3)\fP
True, if
.I expression
is true.
Used to group expressions.
.TP
\f3!\fP \f2expression\fP
True if
.I expression
is false.
.TP
\f2expression1\fP \f3&&\fP \f2expression2\fP
True, if
.I expression1
and
.I expression2
are both true.
.TP
\f2expression1\fP \f3\(bv\(bv\fP \f2expression2\fP
True, if either
.I expression1
or
.I expression2
is true.
.PD
.SS Input/Output.
Before a command is executed, its input and output
may be redirected using a special notation interpreted by the shell.
The following may appear anywhere in a simple-command
or may precede or follow a
.I command
and are
.I not
passed on to the invoked command.
Command substitution, parameter expansion,
and arithmetic substitution occur before
.I word
or
.I digit
is used except as noted below.
File name generation
occurs only if the shell is interactive and
the pattern matches a single file.
Field splitting is not performed.
.PP
In each of the following redirections, if
.I file
is of the form
\f3/dev/tcp/\fP\f2host\fP\f3/\fP\f2port\fP,
or
\f3/dev/udp/\fP\f2host\fP\f3/\fP\f2port\fP,
where
.I host
is a hostname or host address,
and
.I port
is an integer port number,
then the redirection attempts to make a
\f3tcp\fP or \f3udp\fP connection to the corresponding
socket.
.TP 14
.BI < word
Use file
.I word
as standard input (file descriptor 0).
.TP
.BI > word
Use file
.I word
as standard output (file descriptor 1).
If the file does not exist then it is created.
If the file exists, and the
.B noclobber
option is on,
this causes an error;
otherwise, it is truncated to zero length.
.TP
.BI >| word
Sames as
.BR > ,
except that it overrides the
.B noclobber
option.
.TP
.BI >> word
Use file
.I word
as standard output.
If the file exists, then output is appended to it (by first seeking to the end-of-file);
otherwise, the file is created.
.TP
.BI <> word
Open file
.I word
for reading and writing
as standard input.
.TP
\f3<<\fP\*(OK\f3\-\fP\*(CK\f2word\fP
The shell input is read up to a line that is the same as
.IR word
after any quoting has been removed,
or to an end-of-file.
No parameter substitution, command substitution, arithmetic substitution or
file name generation is performed on
.IR word .
The resulting document,
called a
.IR here-document ,
becomes
the standard input.
If any character of
.I word
is quoted, then no interpretation
is placed upon the characters of the document;
otherwise, parameter expansion, command substitution, and arithmetic
substitution occur,
.B \enew-line
is ignored,
and
.B \e
must be used to quote the characters
.BR \e ,
.BR $ ,
.BR \*` .
If
.B \-
is appended to
.BR << ,
then all leading tabs are stripped from
.I word
and from the document.
.TP
.BI <& digit
The standard input is duplicated from file descriptor
.I digit
(see
.IR dup (2)).
Similarly for the standard output using
\f3>&\^\f2digit\fR.
.TP
.BI <& digit \-
The file descriptor given by
.I digit
is moved to standard input.
Similarly for the standard output using
\f3>&\^\f2digit\f3\-\fR.
.TP
.B <&\-
The standard input is closed.
Similarly for the standard output using
.BR >&\- .
.TP
.B <&p
The input from the co-process is moved to standard input.
.TP
.B >&p
The output to the co-process is moved to standard output.
.PP
If one of the above is preceded by a digit,
then the
file descriptor number referred to is that specified
by the digit
(instead of the default 0 or 1).
For example:
.PP
.RS
\fB\&.\|.\|. \|2>&1\fR
.RE
.PP
means file descriptor 2 is to be opened
for writing as a duplicate
of file descriptor 1.
.PP
The order in which redirections are specified is significant.
The shell evaluates each redirection in terms of the
.RI ( "file descriptor" ", " file )
association at the time of evaluation.
For example:
.PP
.RS
\fB\&.\|.\|. \|1>\f2fname\^\fP 2>&1\fR
.RE
.PP
first associates file descriptor 1 with file
.IR fname\^ .
It then associates file descriptor 2 with the file associated with file
descriptor 1 (i.e.
.IR fname\^ ).
If the order of redirections were reversed, file descriptor 2 would be associated
with the terminal (assuming file descriptor 1 had been) and then file descriptor
1 would be associated with file
.IR fname\^ .
.PP
If a command is followed by
.B &
and job control is not active,
then the default standard input
for the command
is the empty file
.BR /dev/null .
Otherwise, the environment for the execution of a command contains the
file descriptors of the invoking shell as modified by
input/output specifications.
.SS Environment.
The
.I environment
(see
.IR environ (7))
is a list of name-value pairs that is passed to
an executed program in the same way as a normal argument list.
The names must be
.I identifiers
and the values are character strings.
The shell interacts with the environment in several ways.
On invocation, the shell scans the environment
and creates a
variable
for each name found,
giving it the corresponding value and attributes and marking it
.IR export .
Executed commands inherit the environment.
If the user modifies the values of these
variables
or creates new ones,
using the
.B export
or
.B typeset \-x
commands, they become part of the
environment.
The environment seen by any executed command is thus composed
of any name-value pairs originally inherited by the shell,
whose values may be modified by the current shell,
plus any additions
which must be noted in
.B export
or
.B typeset \-x
commands.
.PP
The environment for any
.I simple-command
or function
may be augmented by prefixing it with one or more variable assignments.
A variable assignment argument is a word of the form
.IR identifier=value .
Thus:
.PP
.RS
\fB\s-1TERM\s+1=450 \|cmd \|args\fR				and
.br
\fB(export \|\s-1TERM\s+1; \|\s-1TERM\s+1=450; \|cmd \|args)\fR
.RE
.PP
are equivalent (as far as the above execution of
.I cmd
is concerned except for special built-in commands listed below \-
those that are
preceded with a dagger).
.PP
If the obsolete
.B \-k
option is set,
.I all
variable assignment arguments are placed in the environment,
even if they occur after the command name.
The following
first prints
.B "a=b c"
and then
.BR c :
.PP
.RS
.nf
.ft B
echo \|a=b \|c
set \|\-k
echo \|a=b \|c
.ft R
.fi
.RE
This feature is intended for use with scripts written
for early versions of the shell and its use in new scripts
is strongly discouraged.
It is likely to disappear someday.
.SS Functions.
.PP
For historical reasons, there are two
ways to define functions,
the
.IB name (\^)
syntax and
the
.B function
.I name
syntax, described in the
.I Commands
section above.
Shell functions are read in and stored internally.
Alias names are resolved when the function is read.
Functions are executed like commands with the arguments
passed as positional parameters.
(See
.I Execution
below.)
.PP
Functions defined by the
.B function
.I name
syntax and called by name execute in the same process as the caller and
share all files
and present working directory with the
caller.
Traps caught by the caller are reset to their default action
inside the function.
A trap condition that is not caught or ignored by the
function causes the function to terminate and the condition
to be passed on to the caller.
A trap on
.SM
.B EXIT
set inside a function
is executed
in the environment
of the caller
after the function completes.
Ordinarily,
variables are shared between the calling program
and the function.
However,
the
.B typeset
special built-in command used within a function
defines local variables whose scope includes
the current function and
all functions it calls.
Errors within functions return control to the caller.
.PP
Functions defined with the
.IB name (\^)
syntax and functions defined with the
.B function
.I name
syntax that are invoked with the \f3\s+2.\s-2\fP
special built-in
are executed in the caller's
environment and share all variables
and traps with the caller.
Errors within these function executions cause the script that contains
them to abort.
.PP
The special built-in command
.B return
is used to return
from function calls.
.PP
Function names
can be listed with the
.B \-f
or
.B +f
option of the
.B typeset
special built-in command.
The text of functions, when available, will also
be listed with
.BR \-f .
Functions can be undefined with the
.B \-f
option of the
.B unset
special built-in command.
.PP
Ordinarily, functions are unset when the shell executes a shell script.
Functions that need to be defined across separate
invocations of the shell should
be placed in a directory and the
.B
.SM
FPATH
variable should contain the name of this directory.
They may also
be specified in the
.B
.SM
ENV
file.
.SS Discipline Functions.
Each variable can have zero or more discipline functions
associated with it.
The shell initially understands the discipline names \f3get\fP,
\f3set\fP, and \f3unset\fP but on most systems
others can be added at run time via the 
C programming interface extension provided by the
.B builtin
built-in utility.
If the \f3get\fP discipline is defined for a variable, it is invoked
whenever the given variable is referenced.
If the variable \f3.sh.value\fP is assigned a value inside
the discipline function, the referenced variable will evaluate
to this value instead.
If the \f3set\fP discipline is defined for a variable, it is invoked
whenever the given variable is assigned a value.
The variable \f3.sh.value\fP is given the value
of the variable before invoking the discipline, and
the variable will be assigned the value of \f3.sh.value\fP
after the discipline completes.
If \f3.sh.value\fP is unset inside the discipline, then
that value is unchanged.
If the \f3unset\fP discipline is defined for a variable, it is invoked
whenever the given variable is unset.
The variable will not be unset unless it is unset explicitly
from within this discipline function.
.PP
The variable
.B .sh.name
contains the name of the variable for which the discipline function is called,
.B .sh.subscript
is the subscript of the variable, and
.B .sh.value
will contain the value being assigned inside the
.B .set
discipline function.
For the \f3set\fP discipline,
changing
.B .sh.value
will change the value that gets assigned.
.SS Jobs.
.PP
If the
.B monitor
option of the
.B set
command is turned on,
an interactive shell associates a \fIjob\fR with each pipeline.
It keeps
a table of current jobs, printed by the
.B jobs
command, and assigns them small integer numbers.
When a job is started asynchronously with
.BR & ,
the shell prints a line which looks
like:
.PP
.DT
	[1] 1234
.PP
indicating that the job which was started asynchronously was job number
1 and had one (top-level) process, whose process id was 1234.
.PP
This paragraph and the next require features that are
not in all versions of UNIX and may not apply.
If you are running a job and wish to do something else you may hit the key
\fB^Z\fR (control-Z) which sends a STOP signal to the current job.
The shell will then normally indicate that the job has been `Stopped',
and print another prompt.
You can then manipulate the state of this job,
putting it in the background with the
.B bg
command, or run some other
commands and then eventually bring the job back into the foreground with
the foreground command
.BR fg .
A \fB^Z\fR takes effect immediately and
is like an interrupt in that pending output and unread input are discarded
when it is typed.
.PP
A job being run in the background will stop if it tries to read
from the terminal.
Background jobs are normally allowed to produce output,
but this can be disabled by giving the command
.BR "stty tostop" .
If you set this
tty option, then background jobs will stop when they try to produce
output like they do when they try to read input.
.PP
There are several ways to refer to jobs in the shell.
A job can be referred to by the process id of any process of the job
or by one of the following:
.PD 0
.TP
.BI % number
The job with the given number.
.TP
.BI % string
Any job whose command line begins with
.IR string .
.TP
.BI %? string
Any job whose command line contains
.IR string .
.TP
.BI %%
Current job.
.TP
.BI %+
Equivalent to
.BR %% .
.TP
.BI %\-
Previous job.
.PD
.PP
The shell learns immediately whenever a process changes state.
It normally informs you whenever a job becomes blocked so that
no further progress is possible, but only just before it prints
a prompt.
This is done so that it does not otherwise disturb your work.
The
.B notify
option of the
.B set
command causes
the shell to print these job change messages
as soon as they occur.
.PP
When the
.B monitor
option is on, each background job that completes
triggers any trap set for
.BR CHLD .
.PP
When you try to leave the shell while jobs are running or stopped, you will
be warned that `You have stopped(running) jobs.'
You may use the
.B jobs
command to see what they are.
If you immediately try to
exit again, the shell will not warn you a second time, and the stopped
jobs will be terminated.
When a login shell receives a HUP signal, it sends
a HUP signal to each job that has not been disowned with the
.B disown
built-in command described below.
.SS Signals.
The \s-1INT\s+1 and \s-1QUIT\s+1 signals for an invoked
command are ignored if the command is followed by
.B &
and the
.B monitor
option is not active.
Otherwise, signals have the values
inherited by the shell from its parent
(but see also
the
.B trap
built-in command below).
.SS Execution.
Each time a command is read, the above substitutions
are carried out.
If the command name matches one
of the
.I "Special Built-in Commands"
listed below,
it is executed within the
current shell process.
Next, the command name is checked to see if
it matches a user defined function.
If it does,
the positional parameters are saved
and then reset to the arguments of the
.I function
call.
A function is also executed in the
current shell process.
When the
.I function
completes or issues a
.BR return ,
the positional parameter list is restored.
For functions defined with the
.B function
.I name
syntax,
any trap set on
.SM
.B EXIT
within the function is executed.
The exit value of a
.I function
is the value of the last command executed.
If a command name is not a
.I "special built-in command"
or a user defined
.IR function ,
but it is one of the built-in commands listed below,
it is executed in the current shell process.
.PP
The shell variable
.B
.SM PATH
defines the search path for
the directory containing the command.
Alternative directory names are separated by
a colon
.RB ( : ).
The default path is
.B /bin:/usr/bin:
(specifying
.BR /bin ,
.BR /usr/bin ,
and the current directory
in that order).
The current directory can be specified by
two or more adjacent colons, or by a colon
at the beginning or end of the path list.
If the command name contains a \f3/\fP, then the search path
is not used.
Otherwise, each directory in the path is
searched for an executable file that is not a directory.
If the shell
determines that there is a built-in version
of a command corresponding to a given pathname,
this built-in is invoked in the current process.
A process is created and
an attempt is made to execute the command via
.IR exec (2).
If the file has execute permission but is not an
.B a.out
file,
it is assumed to be a file containing shell commands.
A separate shell is spawned to read it.
All non-exported variables are removed in this case.
If the shell command
file doesn't have read permission,
or if the
.I setuid
and/or
.I setgid
bits are set on the file,
then the shell executes an agent whose job it is to
set up the permissions and execute the shell with the
shell command file passed down as an open file.
A parenthesized command is executed in
a sub-shell without removing non-exported variables.
.SS Command Re-entry.
The text of the last
.B
.SM
HISTSIZE
(default 128)
commands entered from a terminal device
is saved in a
.I history
file.
The file
.B \s-1$HOME\s+1/.sh_history
is used if the
.B
.SM
HISTFILE
variable is not set
or if the file it names is not writable.
A shell can access the commands of
all
.I interactive
shells which use the same named
.SM
.BR HISTFILE .
The built-in command
.B hist
is used to list or
edit a portion of this file.
The portion of the file to be edited or listed can be selected by
number or by giving the first character or
characters of the command.
A single command or range of commands can be specified.
If you do not specify an editor program as
an argument to
.B hist
then the value of the variable
.SM
.B HISTEDIT
is used.
If
.SM
.B HISTEDIT
is unset, the obsolete variable
.SM
.B FCEDIT
is used.
If
.SM
.B FCEDIT
is not defined, then
.B /bin/ed
is used.
The edited command(s) is printed and re-executed upon
leaving the editor unless you quit without writing.
The
.B \-s
option
(and in obsolete versions, the editor name
.BR \-\^ )
is used to skip the editing phase and
to re-execute the command.
In this case a substitution parameter of the form
\f2old\fP\f3=\fP\f2new\fP
can be used to modify the command before execution.
For example, with the preset alias
.BR r ,
which is aliased to
.BR "\(fmhist \-s\(fm" ,
typing
`\f3r bad=good c\fP'
will re-execute the most recent command which starts with the letter
.BR c ,
replacing the first occurrence of the string
.B bad
with the string
.BR good .
.SS In-line Editing Options.
Normally, each command line entered from a terminal device is simply
typed followed by a \f3new-line\fP (`RETURN' or `LINE\ FEED').
If either the
.BR emacs ,
.BR gmacs ,
or
.B vi
option is active, the user can edit the command line.
To be in either of these edit modes
.B set
the corresponding
option.
An editing option is automatically selected each time the
.SM
.B VISUAL
or
.SM
.B EDITOR
variable is assigned a value ending in either of these
option names.
.PP
The editing features require that the user's terminal
accept `RETURN' as carriage return without line feed
and that a space (`\ ') must overwrite the current character on
the screen.
.PP
The editing modes implement a concept where the user is looking through a
window at the current line.
The window width is the value of
.SM
.B COLUMNS
if it is defined, otherwise 80.
If the window width is too small to display the prompt and leave
at least 8 columns to enter input, the prompt is truncated from the
left.
If the line is longer than the window width minus two, a mark is
displayed at the end of the window to notify the user.
As the cursor moves and reaches the window boundaries the window will be
centered about the cursor.
The mark is a
.BR > " (<" ,
.BR * )
if the line extends on the
right (left, both) side(s) of the window.
.PP
The search commands in each edit mode provide access to the history file.
Only strings are matched, not patterns, although a leading
.B ^
in the string restricts the match
to begin at the first character in the line.
.PP
Each of the edit modes has an operation to list the files
or commands that match a partially entered word.
When applied to the first word on the line,
or the first word after a
.BR ; , 
.BR \(bv , 
.BR & , 
or
.BR ( , 
and the word does not begin with
.B \(ap
or contain a
.BR / ,
the list of aliases, functions, and executable commands
defined by the
.B
.SM PATH
variable that could match the partial word is displayed.
Otherwise, the list of files that match the given
word is displayed.
If the partially entered word does not contain any
file expansion characters, a
.B *
is appended before generating these lists.
After displaying the generated list, the input line
is redrawn.
These operations are called command name listing and file name listing,
respectively.
There are additional operations, referred to as command name
completion and file name completion, which compute the list
of matching commands or files, but instead of printing the list,
replace
the current word with a complete or partial match.
For file name completion,
if the match is unique, a
.B /
is appended if the file is a directory and a space is
appended if the file is not a directory.
Otherwise, the longest common prefix for all the matching
files replaces the word.
For command name completion, only the portion of the file names
after the last
.B /
are used to find the longest command prefix.
If only a single name matches this prefix, then the
word is replaced with the command name followed by a space.
.SS Key Bindings.
The
.B
.SM KEYBD
trap can be used to intercept keys as they are typed
and change the characters that are actually seen by
the shell.
This trap is executed after each character
(or sequence of characters when the first character is ESC)
is entered while reading from a terminal.
The variable
.B .sh.edchar
contains the character or character sequence which
generated the trap.
Changing the value of
.B .sh.edchar
in the trap action causes the shell to behave as if the
new value were entered from the keyboard rather than
the original value.
.PP
The variable
.B .sh.edcol
is set to the input column number of the cursor at the time
of the input.
The variable
.B .sh.edmode
is set to
ESC
when in
.B vi
insert mode (see below) and is null otherwise.
By prepending
.B ${.sh.editmode}
to a value assigned to
.B .sh.edchar
it will cause the shell
to change to control mode if it is not already in this mode.
.PP
This trap is not invoked for characters entered as arguments to
editing directives, or while reading input for a character search.
.SS Emacs Editing Mode.
This mode is entered by enabling either the
.B emacs
or
.B gmacs
option.
The only difference between these two modes is the way
they handle
.BR ^T .
To edit, the user
moves the cursor to the point needing correction and
then inserts or deletes characters or words as needed.
All the editing commands are control characters or escape
sequences.
The notation for control characters is caret
.RB ( ^ )
followed
by the character.
For example,
.B ^F
is the notation for control
.BR F .
This is entered by depressing `f' while holding down the
`CTRL' (control) key.
The `SHIFT' key is
.I not
depressed.
(The notation
.B ^?
indicates the DEL (delete) key.)
.PP
The notation for escape sequences is
.B M-
followed by a
character.
For example,
.B M-f
(pronounced Meta f)
is entered by depressing ESC
(ascii
.BR 033 )
followed by `f'.
.RB ( M-F
would be the notation for ESC followed by `SHIFT' (capital) `F'.)
.PP
All edit commands
operate from any place on the line
(not just at the beginning).
Neither the `RETURN' nor the `LINE FEED' key is
entered after edit commands except when noted.
.PP
.PD 0
.TP 10
.BI ^F
Move cursor forward (right) one character.
.PP
.TP 10
.BI M-f
Move cursor forward one word.
(The
.B emacs
editor's idea of a word is a string of characters
consisting of only letters, digits and underscores.)
.PP
.TP 10
.BI ^B
Move cursor backward (left) one character.
.PP
.TP 10
.BI M-b
Move cursor backward one word.
.PP
.TP 10
.BI ^A
Move cursor to start of line.
.PP
.TP 10
.BI ^E
Move cursor to end of line.
.PP
.TP 10
.BI ^] char
Move cursor forward to character
.I char
on current line.
.PP
.TP 10
.BI M-^] char
Move cursor backward to character
.I char
on current line.
.PP
.TP 10
.BI ^X^X
Interchange the cursor and mark.
.PP
.TP 10
.I erase
(User defined erase character as defined
by the
.IR stty (1)
command, usually
.B ^H
or
.BR # .)
Delete previous character.
.PP
.TP 10
.BI ^D
Delete current character.
.PP
.TP 10
.BI M-d
Delete current word.
.PP
.TP 10
.BI M-^H
(Meta-backspace) Delete previous word.
.PP
.TP 10
.BI M-h
Delete previous word.
.PP
.TP 10
.BI M-^?
(Meta-DEL) Delete previous word (if your interrupt character is
.B ^?
(DEL, the default) then this command will not work).
.PP
.TP 10
.BI ^T
Transpose current character with previous character
and advance the cursor
in
.I emacs
mode.
Transpose two previous characters in
.I gmacs
mode.
.PP
.TP 10
.BI ^C
Capitalize current character.
.PP
.TP 10
.BI M-c
Capitalize current word.
.PP
.TP 10
.BI M-l
Change the current word to lower case.
.PP
.TP 10
.BI ^K
Delete from the cursor to the end of the line.
If preceded by a numerical parameter whose value is less than the
current cursor position, then delete from given position
up to the cursor.
If preceded by a numerical parameter whose value is greater than the
current cursor position, then delete from cursor up to
given cursor position.
.PP
.TP 10
.BI ^W
Kill from the cursor to the mark.
.PP
.TP 10
.BI M-p
Push the region from the cursor to the mark on the stack.
.PP
.TP 10
.I kill
(User defined kill character as defined
by the stty command, usually
.B ^G
or
.BR @ .)
Kill the entire current line.
If two
.I kill
characters are entered in succession, all
kill characters from then on cause a line feed
(useful when using paper terminals).
.PP
.TP 10
.BI ^Y
Restore last item removed from line. (Yank item back to the line.)
.PP
.TP 10
.BI ^L
Line feed and print current line.
.PP
.TP 10
.BI ^@
(Null character) Set mark.
.PP
.TP 10
.BI M- space
(Meta space) Set mark.
.PP
.TP 10
.BI ^J	
(New\ line) Execute the current line.
.PP
.TP 10
.BI ^M	
(Return) Execute the current line.
.PP
.TP 10
.I eof
End-of-file character,
normally
.BR ^D ,
is processed as an End-of-file only
if the current line is null.
.PP
.TP 10
.BI ^P
Fetch previous command.
Each time
.B ^P
is entered
the previous command back in time is accessed.
Moves back one line when not on the first line of a multi-line command.
.PP
.TP 10
.BI M-<
Fetch the least recent (oldest) history line.
.PP
.TP 10
.BI M->
Fetch the most recent (youngest) history line.
.PP
.TP 10
.BI ^N
Fetch next command line.
Each time
.B ^N
is entered
the next command line forward in time is accessed.
.PP
.TP 10
.BI ^R string
Reverse search history for a previous command line containing
.IR string .
If a parameter of zero is given, the search is forward.
.I String
is terminated by a `RETURN' or `NEW\ LINE'.
If string is preceded by a
.BR ^ ,
the matched line must begin with
.IR string .
If
.I string
is omitted,
then the next command line containing the most recent
.I string
is accessed.
In this case a parameter of zero
reverses the direction of the search.
.PP
.TP 10
.B ^O
Operate \- Execute the current line and fetch
the next line relative to current line from the
history file.
.PP
.TP 10
.BI M- digits
(Escape) Define numeric parameter, the digits
are taken as a parameter to the next command.
The commands that accept a parameter are
.BR ^F ,
.BR ^B ,
.IR erase ,
.BR ^C ,
.BR ^D ,
.BR ^K ,
.BR ^R ,
.BR ^P ,
.BR ^N ,
.BR ^] ,
.BR M-. ,
.BR M-^] ,
.BR M-_ ,
.BR M-b ,
.BR M-c ,
.BR M-d ,
.BR M-f ,
.BR M-h ,
.B M-l
and
.BR M-^H .
.PP
.TP 10
.BI M- letter
Soft-key \- Your alias list is searched for an
alias by the name
.BI _ letter
and if an alias of this name is defined, its
value will be inserted on the input queue.
The
.I letter
must not be one of the above meta-functions.
.PP
.TP 10
.BI M-[ letter
Soft-key \- Your alias list is searched for an
alias by the name
.BI _\&_ letter
and if an alias of this name is defined, its
value will be inserted on the input queue.
The can be used to program functions keys on many terminals.
.PP
.TP 10
.B M-.
The last word of the previous command is inserted
on the line.
If preceded by a numeric parameter, the value
of this parameter determines which word to insert rather than
the last word.
.PP
.TP 10
.B M-_
Same as
.BR M-. .
.PP
.TP 10
.B M-*
Attempt file name generation on the current word.
An asterisk is appended if the word doesn't match any file
or contain any special
pattern characters.
.PP
.TP 10
.B M-ESC
Command or file name completion as described above.
.PP
.TP 10
.B M-=
Command or file name listing as described above.
.PP
.TP 10
.BI ^U
Multiply parameter of next command by 4.
.PP
.TP 10
.BI \e
Escape next character.
Editing characters, the user's erase, kill and
interrupt (normally
.BR ^? )
characters
may be entered
in a command line or in a search string if preceded by a
.BR \e .
The
.B \e
removes the next character's
editing features (if any).
.PP
.TP 10
.B ^V
Display version of the shell.
.PP
.TP 10
.B M-#
If the line does not begin with a
.BR # ,
a
.B #
is inserted
at the beginning of the line
and after each new-line,
and the line is entered.
This causes a comment to be inserted in the history file.
If the line begins with a
.BR # ,
the 
.B #
is deleted and one 
.B #
after each new-line is also deleted.
.PD
.SS Vi Editing Mode.
There are two typing modes.
Initially, when you enter a command you are in the
.I input
mode.
To edit, the user enters
.I control
mode by typing ESC
.RB ( 033 )
and moves the cursor to the point needing correction and
then inserts or deletes characters or words as needed.
Most control commands accept an optional repeat
.I count
prior to the command.
.PP
When in
.B vi
mode on most systems,
canonical processing is initially enabled and the
command will be echoed again if the speed is 1200 baud or greater and it
contains any control characters or less than one second has elapsed
since the prompt was printed.
The ESC character terminates canonical processing for the remainder of the command
and the user can then modify the command line.
This scheme has the advantages of canonical processing with the type-ahead
echoing of raw mode.
.PP
If the option
.B viraw
is also set, the terminal will always have canonical processing
disabled.
This mode is implicit for systems that do not support two
alternate end of line delimiters,
and may be helpful for certain terminals.
.SS "\ \ \ \ \ Input Edit Commands"
.PP
.RS
By default the editor is in input mode.
.PD 0
.TP 10
.I erase
(User defined erase character as defined
by the stty command, usually
.B ^H
or
.BR # .)
Delete previous character.
.TP 10
.BI ^W
Delete the previous blank separated word.
On some systems the \f3viraw\fP option
may be required for this to work.
.TP 10
.I eof
As the first character of the line causes
the shell to terminate unless the \f3ignoreeof\fP
option is set.
Otherwise this character is ignored.
.TP 10
.BI ^V
Escape next character.
Editing characters and the user's erase or kill
characters may be entered
in a command line or in a search string if preceded by a
.BR ^V .
The
.B ^V
removes the next character's
editing features (if any).
On some systems the \f3viraw\fP option
may be required for this to work.
.TP 10
.BI \e
Escape the next
.I erase
or
.I kill
character.
.RE
.SS "\ \ \ \ \ Motion Edit Commands"
.RS
These commands will move the cursor.
.TP 10
[\f2count\fP]\f3l\fP
Cursor forward (right) one character.
.TP 10
[\f2count\fP]\f3w\fP
Cursor forward one alpha-numeric word.
.TP 10
[\f2count\fP]\f3W\fP
Cursor to the beginning of the next word that follows a blank.
.TP 10
[\f2count\fP]\f3e\fP
Cursor to end of word.
.TP 10
[\f2count\fP]\f3E\fP
Cursor to end of the current blank delimited word.
.TP 10
[\f2count\fP]\f3h\fP
Cursor backward (left) one character.
.TP 10
[\f2count\fP]\f3b\fP
Cursor backward one word.
.TP 10
[\f2count\fP]\f3B\fP
Cursor to preceding blank separated word.
.TP 10
[\f2count\fP]\f3\(bv\fP
Cursor to column
.IR count .
.TP 10
[\f2count\fP]\f3f\fP\f2c\fP
Find the next character \fIc\fP in the current line.
.TP 10
[\f2count\fP]\f3F\fP\f2c\fP
Find the previous character \fIc\fP in the current line.
.TP 10
[\f2count\fP]\f3t\fP\f2c\fP
Equivalent to
.B f
followed by
.BR h .
.TP 10
[\f2count\fP]\f3T\fP\f2c\fP
Equivalent to
.B F
followed by
.BR l .
.TP 10
[\f2count\fP]\f3;\fP
Repeats
.I count
times,
the last single character find command,
.BR f ,
.BR F ,
.BR t ,
or
.BR T .
.TP 10
[\f2count\fP]\f3,\fP
Reverses the last single character find command
.I count
times.
.TP 10
.B 0
Cursor to start of line.
.TP 10
.B ^
Cursor to first non-blank character in line.
.TP 10
.B $
Cursor to end of line.
.TP 10
.B %
Moves to balancing
.BR ( ,
.BR ) ,
.BR { ,
.BR } ,
.BR [ ,
or
.BR ] .
If cursor is not on one of the above characters,
the remainder of the line is searched for the first
occurrence of one of the above characters first.
.RE
.SS "\ \ \ \ \ Search Edit Commands"
.RS
These commands access your command history.
.TP 10
[\f2count\fP]\f3k\fP
Fetch previous command.
Each time
.B k
is entered
the previous command back in time is accessed.
.TP 10
[\f2count\fP]\f3\-\fP
Equivalent to
.BR k .
.TP 10
[\f2count\fP]\f3j\fP
Fetch next command.
Each time
.B j
is entered
the next command forward in time is accessed.
.TP 10
[\f2count\fP]\f3+\fP
Equivalent to
.BR j .
.TP 10
[\f2count\fP]\f3G\fP
The command number
.I count
is fetched.
The default is the least recent history command.
.TP 10
.BI / string
Search backward through history for a previous command containing
.IR string .
.I String
is terminated by a `RETURN' or `NEW\ LINE'.
If string is preceded by a
.BR ^ ,
the matched line must begin with
.IR string .
If \fIstring\fP is null, the previous string will be used.
.TP 10
.BI ? string
Same as
.B /
except that search will be in the forward direction.
.TP 10
.B n
Search for next match of the last pattern to
.B /
or
.B ?
commands.
.TP 10
.B N
Search for next match of the last pattern to
.B /
or
.BR ? ,
but in reverse direction.
.RE
.SS "\ \ \ \ \ Text Modification Edit Commands"
.RS
These commands will modify the line.
.TP 10
.B a
Enter input mode and enter text after the current character.
.TP 10
.B A
Append text to the end of the line.
Equivalent to
.BR $a .
.TP 10
[\f2count\fP]\f3c\fP\f2motion\fP
.TP 10
\f3c\fP[\f2count\fP]\f2motion\fP
Delete current character through the character that
.I motion
would move the cursor to and enter input mode.
If \fImotion\fP is
.BR c ,
the entire line will be deleted and
input mode entered.
.TP 10
.B C
Delete the current character through the end of line and enter input mode.
Equivalent to
.BR c$ .
.TP 10
.B S
Equivalent to
.BR cc .
.TP 10
[\f2count\fP]\f3s\fP
Replace characters under the cursor in input mode.
.TP 10
.B D
Delete the current character through the end of line.
Equivalent to
.BR d$ .
.TP 10
[\f2count\fP]\f3d\fP\f2motion\fP
.TP 10
\f3d\fP[\f2count\fP]\f2motion\fP
Delete current character through the character that
.I motion
would move to.
If \fImotion\fP is
.B d ,
the entire line will be deleted.
.TP 10
.B i
Enter input mode and insert text before the current character.
.TP 10
.B I
Insert text before the beginning of the line.
Equivalent to
.BR 0i .
.TP 10
[\f2count\fP]\f3P\fP
Place the previous text modification before the cursor.
.TP 10
[\f2count\fP]\f3p\fP
Place the previous text modification after the cursor.
.TP 10
.B R
Enter input mode and
replace characters on the screen with characters you type overlay fashion.
.TP 10
[\f2count\fP]\f3r\fP\f2c\fP
Replace the
.I count
character(s) starting at the current cursor position with
.IR c ,
and advance the cursor.
.TP 10
[\f2count\fP]\f3x\fP
Delete current character.
.TP 10
[\f2count\fP]\f3X\fP
Delete preceding character.
.TP 10
[\f2count\fP]\f3.\fP
Repeat the previous text modification command.
.TP 10
[\f2count\fP]\f3\(ap\fP
Invert the case of the
.I count
character(s) starting at the current cursor position and advance the cursor.
.TP 10
[\f2count\fP]\f3_\fP
Causes the
.I count
word of the previous command to be appended and
input mode entered.
The last word is used
if
.I count
is omitted.
.TP 10
.B *
Causes an
.B *
to be appended to the current word and file name generation attempted.
If no match is found,
it rings the bell.
Otherwise, the word is replaced
by the matching pattern and input mode is entered.
.TP 10
.B \e 
Command or file name completion as described above.
.RE
.SS "\ \ \ \ \ Other Edit Commands"
.RS
Miscellaneous commands.
.TP 10
[\f2count\fP]\f3y\fP\f2motion\fP
.TP 10
\f3y\fP[\f2count\fP]\f2motion\fP
Yank current character through character that
.I motion
would move the cursor to and puts them into the delete buffer.
The text and cursor are unchanged.
.TP 10
.B yy
Yanks the entire line.
.TP 10
.B Y
Yanks from current position to end of line.
Equivalent to
.BR y$ .
.TP 10
.B u
Undo the last text modifying command.
.TP 10
.B U
Undo all the text modifying commands performed on the line.
.TP 10
[\f2count\fP]\f3v\fP
Returns the command
.BI "hist \-e ${\s-1VISUAL\s+1:\-${\s-1EDITOR\s+1:\-vi}}" " count"
in the input buffer.
If
.I count
is omitted, then the current line is used.
.TP 10
.BI ^L
Line feed and print current line.
Has effect only in control mode.
.TP 10
.BI ^J	
(New\ line) Execute the current line, regardless of mode.
.TP 10
.BI ^M	
(Return) Execute the current line, regardless of mode.
.TP 10
.B #
If the first character of the command is a
.BR # ,
then this command deletes this
.B # 
and each
.B # 
that follows a newline.
Otherwise,
sends the line after
inserting a
.B #
in front of each line in the command.
Useful for causing the current line to be
inserted in the history as a comment and
uncommenting previously commented commands
in the history file.
.TP 10
.B =	
Command or file name listing as described above.
.TP 10
.BI @ letter
Your alias list is searched for an
alias by the name
.BI _ letter
and if an alias of this name is defined, its
value will be inserted on the input queue for processing.
.TP 10
.BI ^V
Display version of the shell.
.RE
.PD
.SS Built-in Commands.
The following simple-commands are executed in the shell process.
Input/Output redirection is permitted.
Unless otherwise indicated, the output is written on file descriptor 1
and the exit status, when there is no syntax error, is zero.
Except for
.BR : ,
.BR true ,
.BR false ,
.BR echo ,
.BR command ,
.BR newgrp ,
and
.BR login ,
all built-in commands accept
.B \-\-
to indicate end of options.
They also interpret the option
.B \-?
as a help request and print a
.I usage
message
on standard error.
Commands that are preceded by one or two \(dg symbols
are
.RI "special built-in commands" ""
and are treated specially in the following ways:
.PD 0
.TP
1.
Variable assignment lists preceding the command
remain in effect when the command completes.
.TP
2.
I/O redirections are processed after variable assignments.
.TP
3.
Errors
cause a script
that contains them to abort.
.TP
4.
They are not valid function names.
.TP
5.
Words
following a command preceded by \(dg\(dg
that are in the format of a variable assignment
are expanded with the same rules as a variable assignment.
This means that
tilde substitution is performed after the
.B =
sign and field splitting and file name generation are not
performed.
.PD
.TP
\(dg \f3:\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
The command only expands parameters.
.br
.ne 2
.TP
\(dg \f3\|. \f2name\^\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
If
.I name
is a function defined with the
.B function
.I name
reserved word syntax,
the function is executed in the current environment
(as if it had been defined with the
.IB name ()
syntax.)
Otherwise if
.I name
refers to a file, the
file is read in its entirety and the commands are
executed in the current shell environment.
The search path
specified by
.B
.SM PATH
is used to find the directory containing the file.
If any arguments
.I arg
are given,
they become the positional parameters while processing
the
.B .
command and the original positional parameters are restored upon completion.
Otherwise the positional parameters are unchanged.
The exit status is the exit status of the last command executed.
.TP
\(dg\(dg \f3alias\fP \*(OK \f3\-ptx\fP \*(CK  \*(OK \f2name\fP\*(OK \f3=\fP\f2value\^\fP  \*(CK \*(CK .\|.\|.
.B alias
with no arguments prints the list of aliases
in the form
.I name=value
on standard output.
The
.B \-p
option
causes the word
.B alias
to be inserted before each one.
When one or more arguments are given,
an
.I alias
is defined
for each
.I name
whose
.I value
is given.
A trailing space in
.I value
causes the next word to be checked for
alias substitution.
The obsolete
.B \-t
option is used to set and list tracked aliases.
The value of a tracked alias is the full pathname
corresponding to the given
.IR name .
The value becomes undefined when the value of
.SM
.B PATH
is reset but the alias remains tracked.
Without the
.B \-t
option,
for each
.I name
in the argument list
for which no
.I value
is given, the name
and value of the alias is printed.
The obsolete
.B \-x
option has no effect.
The exit status is non-zero if a
.I name
is given, but no value, and no alias has been defined for the
.IR name\^ .
.TP
\f3bg\fP \*(OK \f2job\^\fP.\|.\|. \*(CK
This command is only on systems that support job control.
Puts each specified
.I job
into the background.
The current job is put in the background
if
.I job
is not specified.
See
.I Jobs
for a description of the format of
.IR job .
.TP
\(dg \f3break\fP \*(OK \f2n\^\fP \*(CK
Exit from the enclosing
.BR for\^ ,
.BR while\^ ,
.BR until\^ ,
or
.B select
loop, if any.
If
.I n
is specified, then break
.I n
levels.
.TP
\f3builtin\fP \*(OK \f3\-ds\fP \*(CK \*(OK \f3\-f\fP \f2file\^\fP \*(CK \*(OK \f2name\^\fP .\|.\|. \*(CK
If
.I name
is not specified,
and no
.B \-f
option is specified,
the built-ins are printed on standard output.
The
.B \-s
option prints only the special built-ins.
Otherwise, each
.I name
represents the pathname whose basename is the name of the built-in.
The entry point function name is determined by prepending
.B b_
to the built-in name.
Special built-ins cannot be bound to a pathname or deleted.
The
.B \-d
option deletes each of the given built-ins.
On systems that support dynamic loading, the
.B \-f
option names a shared library containing the code for built-ins.
Once a library is loaded, its symbols become available
for subsequent invocations of
.BR builtin .
Multiple libraries can be specified with separate invocations
of the
.B builtin
command.
Libraries are searched in the reverse order in which they are specified.
When a library is loaded, it looks for a function in the library
whose name is
.B lib_init()
and invokes this function with an argument of
.BR 0 .
.TP
.PD 0
\f3cd\fP \*(OK \f3\-LP\fP \*(CK \*(OK \f2arg\^\fP \*(CK
.TP
\f3cd\fP \*(OK \f3\-LP\fP \*(CK \f2old\^\fP \f2new\^\fP
.PD
This command can be in either of two forms.
In the first form it
changes the current directory to
.IR arg .
If
.I arg
is
.B \-
the directory is changed to the previous
directory.
The shell
variable
.B
.SM HOME
is the default
.IR arg .
The variable
.SM
.B PWD
is set to the current directory.
The shell variable
.B
.SM CDPATH
defines the search path for
the directory containing
.IR arg .
Alternative directory names are separated by
a colon
.RB ( : ).
The default path is
.B <null>
(specifying the current directory).
Note that the current directory is specified by a null path name,
which can appear immediately after the equal sign
or between the colon delimiters anywhere else in the path list.
If
.I arg
begins with a \f3/\fP then the search path
is not used.
Otherwise, each directory in the path is
searched for
.IR arg .
.sp .5
The second form of
.B cd
substitutes the string
.I new
for the string
.I old
in the current directory name,
.SM
.BR PWD ,
and tries to change to this new directory.
.sp .5
By default, symbolic link names are treated literally when
finding the directory name.
This is equivalent to the
.B \-L
option.
The
.B \-P
option causes
symbolic links to be resolved when determining the directory.
The last instance of
.B \-L
or
.B \-P
on the command line
determines which method is used.
.sp .5
The
.B cd
command may not be executed by
.if \nZ=0 .B rsh\^.
.if \nZ=1 .B rksh\^.
.TP
\f3command\fP \*(OK \f3\-pvV\fP \*(CK \f2name\^\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
Without the
.B \-v
or
.B \-V
options,
.B command
executes
.I name
with the arguments given by
.IR arg .
The
.B \-p
option causes
a default path to be searched
rather than the one defined by the value of
.SM
.BR PATH .
Functions will not be searched for when finding 
.IR name .
In addition, if
.I name
refers to a special built-in,
none of the special properties associated with the leading
daggers will be honored.
(For example, the predefined alias
.B "redirect=\(fmcommand exec\(fm"
prevents a script from terminating when an invalid
redirection is given.)
With the
.B \-v
option,
.B command
is equivalent to the built-in
.B whence
command described below.
The
.B \-V
option causes
.B command
to act like
.BR "whence \-v" .
.TP
\(dg \f3continue\fP \*(OK \f2n\^\fP \*(CK
Resume the next iteration of the enclosing
.BR for\^ ,
.BR while\^ ,
.BR until\^ ,
or
.B select
loop.
If
.I n
is specified, then resume at the
.IR n -th
enclosing loop.
.TP
\f3disown\fP \*(OK \f2job\^\fP.\|.\|. \*(CK
Causes the shell not to send a HUP signal to
each given
.IR job ,
or all active jobs if
.I job
is omitted,
when a login shell terminates.
.TP
\f3echo\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
When the first
.I arg
does not begin with a \-, and
none of the arguments contain a \e,
then
.B echo
prints each of its arguments separated by a space
and terminated by a new-line.
Otherwise, the behavior of
.B echo
is system dependent
and
.B print
or
.B printf
described below should be used.
See
.IR echo (1)
for usage and description.
.TP
\(dg \f3eval\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
The arguments are read as input
to the shell
and the resulting command(s) executed.
.TP
\(dg \f3exec\fP \*(OK \f3\-c\fP \*(CK \*(OK \f3\-a\fP \f2name\^\fP \*(CK \*(OK \f2arg\^\fP .\|.\|. \*(CK
If
.I arg
is given,
the command specified by
the arguments is executed in place of this shell
without creating a new process.
The
.B \-c
option causes the environment to be cleared before applying
variable assignments associated with the
.B exec
invocation.
The
.B \-a
option
causes
.I name
rather than the first
.IR arg ,
to become
.B argv[0]
for the new process.
Input/output arguments may appear and
affect the current process.
If
.I arg
is not given,
the effect of this command is to
modify file descriptors
as prescribed by the input/output redirection list.
In this case,
any file descriptor numbers greater than 2 that are
opened with this mechanism are closed when invoking
another program.
.TP
\(dg \f3\s-0'exit'\fP \*(OK \f2n\^\fP \*(CK
Causes the shell to exit
with the exit status specified by
.IR n .
The value will be the least significant 8 bits of the specified status.
If
.I n
is omitted, then the exit status is that of the last command executed.
An end-of-file will also cause the shell to exit
except for a
shell which has the
.B ignoreeof
option (see
.B set
below) turned on.
.TP
\(dg\(dg \f3export\fP \*(OK \f3\-p\fP \*(CK \*(OK \f2name\^\fP\*(OK\f3=\fP\f2value\^\fP\*(CK \*(CK .\|.\|.
If
.I name
is not given,
the names and values of each variable with
the export attribute are printed with the values
quoted in a manner that allows them to be re-input.
The
.B \-p
option
causes the word
.B export
to be inserted before each one.
Otherwise, the given
.IR name s
are marked for automatic
export to the
.I environment
of subsequently-executed commands.
.TP
\f3false\fP
Does nothing, and exits 1. Used with
.B until
for infinite loops.
.TP
\f3fg\fP \*(OK \f2job\^\fP.\|.\|. \*(CK
This command is only on systems that support job control.
Each
.I job
specified is brought to the foreground and waited for in
the specified order.
Otherwise, the current job is
brought into the foreground.
See
.I Jobs
for a description of the format of
.IR job .
.TP
\f3getconf\fP \*(OK \f2name\^\fP \*(OK \f2pathname\^\fP \*(CK \*(CK
Prints the current value of the configuration parameter given by
.IR name .
The configuration parameters are defined by the IEEE POSIX 1003.1
and IEEE POSIX 1003.2 standards.
(See
.IR pathconf (2)
and
.IR sysconf (2).)
The
.I pathname
argument is required for parameters whose value depends on
the location in the file system.
If no arguments are given,
.B getconf
prints the names and values of the current configuration
parameters.
The pathname
.B /
is used for each of the parameters that requires
.IR pathname .
.TP
\f3getopts\fP \*(OK \f3\ -a\fP \f2name\^\fP \*(CK \f2optstring vname\^\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
Checks
.I arg
for legal options.
If
.I arg
is omitted,
the positional parameters are used.
An option argument begins with a
.B +
or a
.BR \- .
An option not beginning with
.B +
or 
.B \-
or the argument
.B \-\|\-
ends the options.
.I optstring
contains the letters that
.B getopts
recognizes.
If a letter is followed by a
.BR : ,
that option is expected to have an argument.
The options can be separated from the argument by blanks.
The option
.B \-?
causes
.B getopts
to generate a usage message on standard error.
The
.B \-a
argument can be used to specify the name to use for the
usage message, which defaults to
.BR $0 .
.sp .5
.B
getopts
places the next option letter it finds inside variable
.I vname
each time it is invoked.
The option letter will be prepended with a
.B +
when
.I arg
begins with a
.BR + .
The index of the next
.I arg
is stored in
.SM
.BR OPTIND .
The option argument,
if any,
gets stored in
.SM
.BR OPTARG .
.sp .5
A leading
.B :
in
.I optstring
causes
.B getopts
to store the letter of an invalid
option in
.SM
.BR OPTARG ,
and to set
.I vname
to
.B ?
for an unknown option and to
.B :
when a required option is missing.
Otherwise,
.B getopts
prints an error message.
The exit status is non-zero when there are no more options.
.sp .5
There is no way to specify any of the options
.BR : ,
.BR + ,
.BR \- ,
.BR ? ,
.BR [ ,
and
.BR ] .
The option
.B #
can only be specified as the first option.
.TP
.PD 0
\f3hist\fP \*(OK \f3\-e\fP \f2ename\^\fP \ \*(CK \*(OK \f3\-nlr\^\fP \*(CK \*(OK \f2first\^\fP \*(OK \f2last\^\fP \*(CK \*(CK
.TP
\f3hist \-s \fP \*(OK \f2old\fP\f3\=\fP\f2new\^\fP \*(CK \*(OK \f2command\^\fP \*(CK
.PD
In the first form,
a range of commands from
.I first
to
.I last
is selected from the last
.SM
.B HISTSIZE
commands that were typed at the terminal.
The arguments
.I first
and
.I last
may be specified as a number or as a string.
A string is used to locate the most recent command starting with
the given string.
A negative number is used as an offset to the current command number.
If the
.B \-l
option
is selected,
the commands are listed on standard output.
Otherwise, the editor program
.I ename
is invoked on a file containing these
keyboard commands.
If
.I ename
is not supplied, then the value of the variable
.SM
.B HISTEDIT
is used.
If 
.SM
.B HISTEDIT
is not set, then
.SM
.B FCEDIT
(default
.BR /bin/ed\^ )
is used as the editor.
When editing is complete, the edited command(s)
is executed if the changes have been saved.
If
.I last
is not specified,
then it will be set to
.IR first .
If
.I first
is not specified,
the default is the previous command
for editing and \-16 for listing.
The option
.B \-r
reverses the order of the commands and
the option
.B \-n
suppresses command numbers when listing.
In the second form,
.I command
is interpreted as
.I first
described above
and defaults to the last command executed.
The resulting command is executed
after the optional substitution
\f2old\^\fP\f3=\fP\f2new\^\fP
is performed.
.TP
\f3jobs\fP \*(OK \f3\-lnp\^\fP \*(CK \*(OK \f2job\^\fP \.\|.\|. \*(CK
Lists information about each given job; or all active jobs if
.I job
is omitted.
The
.B \-l
option lists process ids in addition to the normal information.
The
.B \-n
option only displays jobs that have stopped or exited since last
notified.
The
.B \-p
option causes only the process group to be listed.
See
.I Jobs
for a description of the format of
.IR job .
.TP
.PD 0
\f3kill\fP \*(OK \f3\-s\fP \f2signame\^\fP \*(CK \f2job\^\fP .\|.\|.
.TP
.PD 0
\f3kill\fP \*(OK \f3\-n\fP \f2signum\^\fP \*(CK \f2job\^\fP .\|.\|.
.TP
\f3kill\fP \f3\-l\fP \*(OK \f2sig\^\fP .\|.\|. \*(CK
.PD
Sends either the TERM (terminate) signal or the
specified signal to the specified jobs or processes.
Signals are either given by number with the
.B \-n
option or by name with the
.B \-s
option
(as given in
.BR <signal.h> ,
stripped of the prefix ``SIG'' with
the exception that SIGCLD is named CHLD).
For backward compatibility, the
.B n
and
.B s
can be omitted and the number or name placed immediately
after the
.BR \- .
If the signal being sent is TERM (terminate) or HUP (hangup),
then the job or process will be sent a CONT (continue) signal
if it is stopped.
The argument
.I job
can be the process id of a process that is not a member of one of the
active jobs.
See
.I Jobs
for a description of the format of
.IR job .
In the third form,
.BR "kill \-l" ,
if
.I sig
is not specified,
the signal names are listed.
Otherwise, for each
.I sig
that is a name, the corresponding signal number is listed.
For each
.I sig
that is a number, the signal name corresponding to the
least significant 8 bits of
.I sig
is listed.
.TP
\f3let\fP \f2arg\^\fP .\|.\|.
Each
.I arg
is a separate
.I "arithmetic expression"
to be evaluated.
See
.I "Arithmetic Evaluation"
above, for a description of arithmetic expression evaluation.
.sp .5
The exit status is
0 if the value of the last expression
is non-zero, and 1 otherwise.
.TP
\(dg \f3newgrp\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
Equivalent to
.BI "exec /bin/newgrp" " arg\^"
\&.\|.\|.\^.
.TP
\f3print\fP \*(OK \f3\-Rnprs\^\fP \*(CK \*(OK \f3\-u\fP \f2unit\^\fP\*(CK \*(OK \f3\-f\fP \f2format\^\fP \*(CK \*(OK \f2arg\^\fP .\|.\|. \*(CK
With no options or with option
.B \-
or
.BR \-\|\- ,
each
.I arg
is printed
on standard output.
The
.B \-f
option causes the arguments to be printed as
described by
.BR printf .
In this case, any
.BR n ,
.BR r ,
.B R
options are ignored.
Otherwise,
unless the
.B \-R
or
.BR \-r ,
are specified, the following
escape conventions will be applied:
.RS
.PD 0
.TP
.B \ea
The alert character (ascii
.BR 07 ).
.TP
.B \eb
The backspace character (ascii
.BR 010 ).
.TP
.B \ec
Causes
.B print
to end without processing more arguments and
not adding a new-line.
.TP
.B \ef
The formfeed character (ascii
.BR 014 ).
.TP
.B \en
The new-line character (ascii
.BR 012 ).
.TP
.B \er
The carriage return character (ascii
.BR 015 ).
.TP
.B \et
The tab character (ascii
.BR 011 ).
.TP
.B \ev
The vertical tab character (ascii
.BR 013 ).
.TP
.B \eE
The escape character (ascii
.BR 033 ).
.TP
.B \e\e
The backslash character \e.
.TP
.BI \e0 x
The character defined by the 1, 2, or 3-digit octal
string given by \fIx\fP.
.PD
.PP
The
.B \-R
option will print all subsequent arguments and options
other than
.BR \-n .
The
.B \-p
option causes the
arguments to be written onto the pipe
of the process spawned with
.B \(bv&
instead of standard output.
The
.B \-s
option causes the
arguments to be written onto the history file
instead of standard output.
The
.B \-u
option can be used to specify a one digit
file descriptor unit number
.I unit
on which the
output will be placed.
The default is 1.
If the option
.B \-n
is used, no
.B new-line
is added to the output.
.RE
.TP
\f3printf\fP \f2format\^\fP \*(OK \f2arg\^\fP .\|.\|. \*(CK
The arguments
.I arg
are printed on standard output
in accordance with the ANSI-C
formatting rules associated with the format string
.IR format .
If the number of arguments exceeds the number of
format specifications, the
.B format
string is reused to format remaining arguments.
The following extensions can also be used:
.RS
.TP
\(bu
A
.B %b
format can be used instead of
.B %s
to cause escape sequences in the corresponding
.I arg
to be expanded as described in
.BR print.
.TP
\(bu
A
.B %P
format can be used instead of
.B %s
to cause
.I arg
to be interpreted as an extended regular
expression and be printed as a shell pattern.
.TP
\(bu
A
.B %q
format can be used instead of
.B %s
to cause the resulting string to be quoted in a manner than can
be reinput to the shell.
.TP
\(bu
The precision field of the
.B %d
format can be followed by a
.B .
and the output base.
.RE
.TP
\f3pwd\fP \*(OK \f3\-LP\fP \*(CK
Outputs the value of the current working
directory.
The
.B \-L
option is the default; it prints the logical name of the current directory.
If the
.B \-P
option is given,
all symbolic links are resolved from the name.
The last instance of
.B \-L
or
.B \-P
on the command line
determines which method is used.
.TP
\f3read\fP \*(OK \f3\-Aprs\^\fP \*(CK \*(OK \f3\-d\fP \f2delim\^\fP\*(CK \*(OK \f3\-t\fP \f2timeout\^\fP\*(CK \*(OK \f3\-u\fP \f2unit\^\fP\*(CK \*(OK \f2vname\fP\f3?\f2prompt\^\fP \*(CK \*(OK \f2vname\^\fP .\|.\|. \*(CK
The shell input mechanism.
One line is read and
is broken up into fields using the characters in
.B
.SM IFS
as separators.
The escape character,
.BR \e ,
is used to remove any special meaning for the next
character and for line continuation.
The
.B \-d
option
causes the read to continue to the first character of
.I delim
rather than new-line.
In raw mode,
.B \-r,
the
.B \e
character is not treated specially.
The first
field is assigned to the first
.IR vname ,
the second field
to the second
.IR vname ,
etc., with leftover fields assigned to the last
.IR vname .
The
.B \-A
option causes the variable
.I vname
to be unset and each field that is read to be stored in
successive elements of the indexed array
.IR vname.
The
.B \-p
option causes the input line
to be taken from the input pipe
of a process spawned by the shell
using
.BR \(bv& .
If the
.B \-s
option is present,
the input will be saved as a command in the history file.
The option
.B \-u
can be used to specify a one digit file
descriptor unit
.I unit
to read from.
The file descriptor can be opened with the
.B exec
special built-in command.
The default value of unit
.I n
is 0.
The option
.B \-t
is used to specify a timeout in
seconds when reading from a terminal or pipe.
If
.I vname
is omitted, then
.SM
.B REPLY
is used as the default
.IR vname .
An end-of-file with the
.B \-p
option causes cleanup for this process
so that another can be spawned.
If the first argument contains a
.BR ? ,
the remainder of this word is used as a
.I prompt
on standard error
when the shell is interactive.
The exit status is 0 unless an end-of-file is encountered
or
.B read
has timed out.
.TP
\(dg\(dg \f3readonly\fP \*(OK \f3\-p\fP \*(CK \*(OK \f2vname\fP\*(OK\f3=\fP\f2value\^\fP\*(CK \*(CK .\|.\|.
If
.I vname
is not given,
the names and values of each variable with
the readonly attribute is printed with the values
quoted in a manner that allows them to be re-inputted.
The
.B \-p
option
causes the word
.B readonly
to be inserted before each one.
Otherwise, the given
.IR vname s
are marked
readonly and these
names cannot be changed
by subsequent assignment.
.TP
\(dg \f3return\fP \*(OK \f2n\^\fP \*(CK
Causes a shell
.I function
or
\f3\|.\fP
script to return
to the invoking script
with the exit status specified by
.IR n .
The value will be the least significant 8 bits of the specified status.
If
.I n
is omitted, then the return status is that of the last command executed.
If
.B return
is invoked while not in a
.I function
or a
\f3\|.\fP
script,
then it behaves the same as
.BR exit .
.TP
\(dg \f3\s-0'set'\fP \*(OK \f3\(+-Cabefhkmnopstuvx\fP \*(CK \*(OK \f3\(+-o\fP \*(OK \f2option\^\fP \*(CK \*(CK .\|.\|. \*(OK \f3\(+-A\fP \f2vname\^\fP \*(CK  \*(OK \f2arg\^\fP .\|.\|. \*(CK
The options for this command have meaning as follows:
.RS
.PD 0
.TP 8
.B \-A
Array assignment.
Unset the variable
.I vname
and assign values sequentially from the
.I arg
list.
If
.B +A
is used, the variable
.I vname
is not unset first.
.TP 8
.B \-C
Prevents redirection
.B >
from truncating existing files.
Files that are created are opened with the O_EXCL mode.
Requires
.B >\(bv
to truncate a file when turned on.
.TP 8
.B \-a
All subsequent variables that are defined are automatically exported.
.TP 8
.B \-b
Prints job completion messages as soon as a background job changes
state rather than waiting for the next prompt.
.TP 8
.B \-e
If a command has a non-zero exit status,
execute the
.SM
.B ERR
trap, if set,
and exit.
This mode is disabled while reading profiles.
.TP 8
.B \-f
Disables file name generation.
.TP 8
.B \-h
Each command
becomes a tracked alias when first encountered.
.TP 8
.B \-k
(Obsolete). All variable assignment arguments are placed in the environment for a command,
not just those that precede the command name.
.TP 8
.B \-m
Background jobs will run in a separate process group
and a line will print upon completion.
The exit status of background jobs is reported in a completion message.
On systems with job control,
this option is turned on automatically for
interactive shells.
.TP 8
.B \-n
Read commands and check them for syntax errors, but do not execute them.
Ignored for interactive shells.
.TP 8
.B \-o
The following argument can be one of the following option names:
.RS
.TP 8
.B allexport
Same as
.BR \-a .
.TP 8
.B errexit
Same as
.BR \-e .
.TP 8
.B bgnice
All background jobs are run at a lower priority.
This is the default mode.
.TP 8
.B emacs
Puts you in an
.I emacs
style in-line editor for command entry.
.TP 8
.B gmacs
Puts you in a
.I gmacs
style in-line editor for command entry.
.TP 8
.B ignoreeof
The shell will not exit on end-of-file.
The command
.B exit
must be used.
.TP 8
.B keyword
Same as
.BR \-k .
.TP 8
.B markdirs
All directory names resulting from file name generation have a trailing
.B /
appended.
.TP 8
.B monitor
Same as
.BR \-m .
.TP 8
.B noclobber
Same as
.BR \-C .
.TP 8
.B noexec
Same as
.BR \-n .
.TP 8
.B noglob
Same as
.BR \-f .
.TP 8
.B nolog
Do not save function definitions in the history file.
.TP 8
.B notify
Same as
.BR \-b .
.TP 8
.B nounset
Same as
.BR \-u .
.TP 8
.B privileged
Same as
.BR \-p .
.TP 8
.B verbose
Same as
.BR \-v .
.TP 8
.B trackall
Same as
.BR \-h .
.TP 8
.B vi
Puts you in insert mode of a
.I vi
style in-line editor
until you hit the escape character
.BR 033 .
This puts you in control mode.
A return sends the line.
.TP 8
.B viraw
Each character is processed as it is typed
in
.I vi
mode.
.TP 8
.B xtrace
Same as
.BR \-x .
.TP 8
If no option name is supplied, then the current option settings are printed.
.RE
.TP 8
.B \-p
Disables processing of the
.B \s-1$HOME\s+1/.profile
file and uses the file
.B /etc/suid_profile
instead of the
.SM
.B ENV
file.
This mode is on whenever the effective uid (gid)
is not equal to the real uid (gid).
Turning this off causes the effective uid and gid to be
set to the real uid and gid.
.TP 8
.B \-s
Sort the positional parameters lexicographically.
.TP 8
.B \-t
(Obsolete).  Exit after reading and executing one command.
.TP 8
.B \-u
Treat unset parameters as an error when substituting.
.TP 8
.B \-v
Print shell input lines as they are read.
.TP 8
.B \-x
Print commands and their arguments as they are executed.
.TP 8
.B \-\|\-
Do not change any of the options; useful in setting
.B $1
to a value beginning with
.BR \- .
If no arguments follow this option then the positional parameters are unset.
.PD
.PP
As an obsolete feature,
if the first
.I arg
is
.B \-
then the
.B \-x
and
.B \-v
options are turned off and the next
.I arg
is treated as the first argument.
Using
.B \+
rather than
.B \-
causes these options to be turned off.
These options can also be used upon invocation of the shell.
The current set of options may be found in
.BR $\- .
Unless
.B \-A
is specified,
the remaining arguments are positional
parameters and are assigned, in order, to
.B $1
.B $2
\&.\|.\|.\^.
If no arguments are given, then the names and values
of all variables are printed on the standard output.
.RE
.TP
\(dg \f3shift\fP \*(OK \f2n\^\fP \*(CK
.br
The positional parameters from
\f3$\fP\f2n\fP\f3+1\fP
\&.\|.\|.
are renamed
.B $1
\&.\|.\|.\^
, default
.I n
is 1.
The parameter
.I n
can be any arithmetic expression that evaluates to a non-negative
number less than or equal to
.BR $# .
.TP
\f3sleep\fP \f2seconds\^\fP
Suspends execution for the number of decimal seconds or fractions of a
second given by
.IR seconds .
.TP
\(dg \f3\s-0trap'\fP \*(OK \f3\-p\fP \*(CK \*(OK \f2action\^\fP \*(CK \*(OK \f2sig\^\fP \*(CK .\|.\|.
The
.B \-p
option causes the trap
action associated with each trap as specified by the arguments
to be printed with appropriate quoting.
Otherwise,
.I action
will be processed as if it were an argument to
.B eval
when the shell
receives signal(s)
.IR sig .
Each
.I sig
can be given as a number or as the name of the signal.
Trap commands are executed in order of signal number.
Any attempt to set a trap on a signal that
was ignored on entry to the current shell
is ineffective.
If
.I action
is omitted and the first
.I sig
is a number, or if
.I action
is
.BR \- ,
then the trap(s) for each
.I sig
are reset
to their original values.
If
.I action
is the null
string then this signal is ignored by the shell and by the commands
it invokes.
If
.I sig
is
.SM
.B ERR
then
.I action
will be executed whenever a command has a non-zero exit status.
If
.I sig
is
.SM
.B DEBUG
then
.I action
will be executed before each command.
If
.I sig
is
.B 0
or
.SM
.B EXIT
and the
.B trap
statement is executed inside the body of a function,
then the command
.I action
is executed
after the function completes.
If
.I sig
is
.B 0
or
.SM
.B EXIT
for a
.B trap
set outside any function
then the command
.I action
is executed
on exit from the shell.
If
.I sig
is
.SM
.BR KEYBD ,
then
.I action
will be executed whenever a key is read
while in
.BR emacs ,
.BR gmacs ,
or
.B vi
mode.
The
.B trap
command
with no arguments prints a list
of commands associated with each signal number.
.TP
\f3true\fP
Does nothing, and exits 0. Used with
.B while
for infinite loops.
.TP
\(dg\(dg \f3typeset\fP \*(OK \f3\(+-AHflnprtux\^\fP \*(CK \*(OK \f3\(+-EFLRZi\*(OK\f2n\^\fP\*(CK \*(CK  \*(OK \f2vname\^\fP\*(OK\f3=\fP\f2value\^\fP \*(CK \^ \*(CK .\|.\|.
Sets attributes and values for shell variables and functions.
When invoked inside a function,
a new instance of the variable
.I vname
is created.
The variable's value and type are restored
when the function completes.
The following list of attributes may be specified:
.RS
.PD 0
.TP
.B \-A
Declares
.I vname
to be an associative array.
Subscripts are strings rather than arithmetic
expressions.
.TP
.B \-E
Declares
.I vname
to be a double precision floating point number.
If
.I n
is non-zero, it defines the number of significant figures
that are used when expanding
.IR vname .
Otherwise, ten significant figures will be used.
.TP
.B \-F
Declares
.I vname
to be a double precision floating point number.
If
.I n
is non-zero, it defines the number of places after the
decimal point that are used when expanding
.IR vname .
Otherwise ten places after the decimal point will be used.
.TP
.B \-H
This option provides UNIX to host-name file mapping on non-UNIX
machines.
.TP
.B \-L
Left justify and remove leading blanks from
.IR value .
If
.I n
is non-zero, it defines the width
of the field,
otherwise it is determined by the width of the value of
first assignment.
When the variable is assigned to, it is
filled on the right with blanks or truncated, if necessary, to
fit into the field.
The
.B \-R
option is turned off.
.TP
.B \-R
Right justify and fill with leading blanks.
If
.I n
is non-zero, it defines the width
of the field,
otherwise it is determined by the width of the value of
first assignment.
The field is left filled with blanks or
truncated from the end if the
variable is reassigned.
The
.B \-L
option is turned off.
.TP
.B \-Z
Right justify and fill with leading zeros if
the first non-blank character is a digit and the
.B \-L
option has not been set.
Remove leading zeros if the
.B \-L
option is also set.
If
.I n
is non-zero, it defines the width
of the field,
otherwise it is determined by the width of the value of
first assignment.
.TP
.B \-f
The names refer to function names rather than
variable names.
No assignments can be made and the only other
valid options are
.BR \-t ,
.B \-u
and
.BR \-x .
The
.B \-t
option
turns on execution tracing for this function.
The
.B \-u
option
causes this function to be marked undefined.
The
.SM
.B FPATH
variable will be searched to find the function definition
when the function is referenced.
.TP
.B \-i
Declares
.I vname
to be represented internally as integer.
The right hand side of an assignment is evaluated as an
arithmetic expression when assigning to an integer.
If
.I n
is non-zero, it defines the output arithmetic base,
otherwise the output base will be ten.
.TP
.B \-l
All upper-case characters are
converted to lower-case.
The upper-case option,
.BR \-u ,
is turned off.
.TP
.B \-n
Declares
.I vname
to be a reference to the variable whose name is
defined by the value of variable
.IR vname .
This is usually used to reference a variable inside
a function whose name has been passed as an argument.
.TP
.B \-r
The given
.IR vname s
are marked
readonly and these
names cannot be changed
by subsequent assignment.
.TP
.B \-t
Tags the variables.
Tags are user definable and have no special
meaning to the shell.
.TP
.B \-u
All lower-case characters are converted
to upper-case.
The lower-case option,
.BR \-l ,
is turned off.
.TP
.B \-x
The given
.IR vname s
are marked for automatic
export to the
.I environment
of subsequently-executed commands.
Variables whose names contain a \fB\s+2.\s-2\fP
cannot be exported.
.PD
.PP
The
.B \-i
attribute cannot be specified along with
.BR \-R ,
.BR \-L ,
.BR \-Z ,
or
.BR \-f .
.PP
Using
.B \+
rather than
.B \-
causes these options to be turned off.
If no
.I vname
arguments are given,
a list of
.I vnames
(and optionally the
.IR values\^ )
of the
.I variables
is printed.
(Using
.B \+
rather than
.B \-
keeps the
values from being printed.)
The
.B \-p
option causes
.B typeset
followed by the option letters
to be printed before each name
rather than the names of the options.
If any option other than
.B \-p
is given,
only those variables
which have all of the given
options are printed.
Otherwise, the
.IR vname s
and
.I attributes
of all
.I variables
are printed.
.RE
.TP
\f3ulimit\fP \*(OK \f3\-HSacdfmnpstv\fP \*(CK \*(OK \f2limit\^\fP \*(CK
Set or display a resource limit.
The available resource limits are listed below.
Many systems do not support one or more of these limits.
The limit for a specified resource is set when
.I limit
is specified.
The value of
.I limit
can be a number in the unit specified below with each resource,
or the value
.BR unlimited .
The
.B \-H
and
.B \-S
options specify whether the hard limit or the
soft limit for the given resource is set.
A hard limit cannot be increased once it is set.  A soft
limit can be increased up to the value of the hard limit.
If neither the
.B H
nor
.B S
options is specified, the limit applies to both.
The current resource limit is printed when 
.I limit
is omitted.
In this case, the soft limit is printed unless
.B H
is specified.
When more than one resource is specified, then the limit
name and unit is printed before the value.
.RS
.PD 0
.TP
.B \-a
Lists all of the current resource limits.
.TP
.B \-c
The number of 512-byte blocks on the size of core dumps.
.TP
.B \-d
The number of K-bytes on the size of the data area.
.TP
.B \-f
The number of 512-byte blocks on files that can be written by the
current process or by child processes (files of any size may be read).
.TP
.B \-m
The number of K-bytes on the size of physical memory.
.TP
.B \-n
The number of file descriptors plus 1.
.TP
.B \-p
The number of 512-byte blocks for pipe buffering.
.TP
.B \-s
The number of K-bytes on the size of the stack area.
.TP
.B \-t
The number of CPU seconds to be used by each process.
.TP
.B \-v
The number of K-bytes for virtual memory.
.PD
.PP
If no option is given,
.B \-f
is assumed.
.RE
.TP
\f3umask\fP \*(OK \f3\-S\fP \*(CK \*(OK \f2mask\^\fP \*(CK
The user file-creation mask is set to
.I mask
(see
.IR umask (2)).
.I mask
can either be an octal number or
a symbolic value as described in
.IR chmod (1). 
If a symbolic value is given,
the new
umask value is the complement of the result of
applying
.I mask
to the complement of the previous umask value.
If
.I mask
is omitted, the current value of the mask is printed.
The
.B \-S
option causes the mode to be printed as a symbolic
value.  Otherwise, the
mask is printed in octal. 
.TP
\(dg \f3unalias\fP \*(OK \f3\-a\fP \*(CK \f2name\^\fP .\|.\|.
The aliases
given by the list of
.IR name s
are removed from the alias list.
The
.B \-a
option causes all the
aliases to be unset.
.TP
\(dg\f3unset\fP \*(OK \f3\-fnv\fP \*(CK \f2vname\^\fP .\|.\|.
The variables given by the list of
.IR vname s
are unassigned,
i.e.,
their values and attributes are erased.
Readonly variables cannot be unset.
If the
.B \-f
option
is set, then the names refer to
.I function
names.
If the
.B \-v
option is set, then the names refer to
.I variable
names.
The
.B \-f
option overrides
.BR \-v .
If
.B \-n
is set and
.I name
is a name reference, then
.I name
will be unset rather than the variable
that it references.
The default is equivalent to
.BR \-v .
Unsetting
.SM
.BR LINENO ,
.SM
.BR MAILCHECK ,
.SM
.BR OPTARG ,
.SM
.BR OPTIND ,
.SM
.BR RANDOM ,
.SM
.BR SECONDS ,
.SM
.BR TMOUT ,
and
.SM
.B _
removes their special meaning even if they are
subsequently assigned to.
.TP
\f3wait\fP \*(OK \f2job\^\fP .\|.\|. \*(CK
Wait for the specified
.I job
and
report its termination status.
If
.I job
is not given, then all currently active child processes are waited for.
The exit status from this command is that of
the last process waited for.
See
.I Jobs
for a description of the format of
.IR job .
.TP
\f3whence\fP \*(OK \f3\-afpv\fP \*(CK \f2name\^\fP .\|.\|.
For each
.IR name ,
indicate how it
would be interpreted if used as a command name.
.sp .5
The
.B \-v
option
produces a more verbose report.
The
.B \-f
options skips the search for functions.
The
.B \-p
option
does a path search for
.I name
even if name is an alias, a function, or a reserved word.
The
.B \-a
option
is similar to the
.B \-v
option but causes
all interpretations of the given name to be reported.
.SS Invocation.
If the shell is invoked by
.IR exec (2),
and the first character of argument zero
.RB ( $0 )
is
.BR \- ,
then the shell is assumed to be a
.I login
shell and
commands are read from
.B /etc/profile
and then from either
.B .profile
in the current directory or
.BR \s-1$HOME\s+1/.profile ,
if either file exists.
Next, for interactive shells, commands are read from
the file named by
performing parameter expansion, command substitution,
and arithmetic substitution on
the value of the environment variable
.SM
.B ENV
if the file exists.
If the
.B \-s
option is not present and
.I arg
is, then a path search is performed on the first
.I arg
to determine the name of the script to execute.
The script
.I arg
must have read permission and any
.I setuid
and
.I setgid
settings will be ignored.
If the script is not found on the path,
.I arg
is processed as if it named a built-in command or function.
Commands are then read as described below;
the following options are interpreted by the shell
when it is invoked:
.PP
.PD 0
.TP 10
.BI \-c
If the
.B \-c
option is present, then
commands are read from the first
.IR arg .
Any remaining arguments become
positional parameters starting at
.BR 0 .
.TP
.B \-s
If the
.B \-s
option is present or if no
arguments remain,
then commands are read from the standard input.
Shell output,
except for the output of the
.I special builtin-in commands
listed above,
is written to
file descriptor 2.
.TP
.B \-i
If the
.B \-i
option is present or
if the shell input and output are attached to a terminal (as told by
.IR tcgetattr (2)),
then this shell is
.IR interactive .
In this case \s-1TERM\s+1 is ignored (so that \f3kill 0\fP
does not kill an interactive shell) and \s-1INTR\s+1 is caught and ignored
(so that
.B wait
is interruptible).
In all cases, \s-1QUIT\s+1 is ignored by the shell.
.TP
.B \-r
If the
.B \-r
option is present, the shell is a restricted shell.
.TP
.B \-D
A list of all double quoted strings that are preceded by a
.B $
will be printed on standard output and the shell will exit.
This set of strings will be subject to language translation
when the locale is not C or POSIX.
No commands will be executed.
.PD
.TP
.BI \-I " filename\^"
The
.B \-R
.I filename
option is used
to generate a cross reference database
that can be used by a separate utility
to find definitions and references for variables and commands. 
.PP
The remaining options and arguments are described under the
.B set
command above.
An optional
.B \-
as the first argument is ignored.
.if \nZ=0 \{.SS Rsh Only.
.I Rsh\}
.if \nZ=1 \{.SS Rksh Only.
.I Rksh\}
is used to set up login names and execution environments whose
capabilities are more controlled than those of the standard shell.
The actions of
.if \nZ=0 .B rsh
.if \nZ=1 .B rksh
are identical to those of
.if \nZ=0 .BR sh\^ ,
.if \nZ=1 .BR ksh\^ ,
except that the following are disallowed:
.RS
.PD 0
.PP
changing directory (see
.IR cd (1)),
.br
setting or unsetting the value or attributes of
.SM
.BR SHELL ,
.SM
.BR ENV ,
or
.SM
.BR PATH\*S,
.br
specifying path or
command names containing
.BR / ,
.br
redirecting output
.RB ( > ,
.BR >| ,
.BR <> ,
and
.BR >> ).
.br
adding or deleting built-in commands.
.PD
.RE
.PP
The restrictions above are enforced
after \f3.profile\fP and the
.SM
.B ENV
files are interpreted.
.PP
When a command to be executed is found to be a shell procedure,
.if \nZ=0 \{.B rsh
invokes
.I sh\^\}
.if \nZ=1 \{.B rksh
invokes
.I ksh\^\}
to execute it.
Thus, it is possible to provide to the end-user shell procedures
that have access to the full power of
the standard shell,
while imposing a limited menu of commands;
this scheme assumes that the end-user does not have write and
execute permissions in the same directory.
.PP
The net effect of these rules is that the writer of the
.B .profile
has complete control over user actions,
by performing guaranteed setup actions
and leaving the user in an appropriate directory
(probably
.I not
the login directory).
.PP
The system administrator often sets up a directory
of commands
(e.g.,
.BR /usr/rbin )
that can be safely invoked by
.if \nZ=0 .BR rsh .
.if \nZ=1 .BR rksh .
.SH EXIT STATUS
Errors detected by the shell, such as syntax errors,
cause the shell
to return a non-zero exit status.
Otherwise, the shell returns the exit status of
the last command executed (see also the
.B exit
command above).
If the shell is being used non-interactively,
then execution of the shell file is abandoned.
Run time errors detected by the shell are reported by
printing the command or function name and the error condition.
If the line number that the error occurred on is greater than one,
then the line number is also printed in square brackets
.RB ( "[]" )
after the command or function name.
.SH FILES
/etc/passwd
.br
/etc/profile
.br
/etc/suid_profile
.br
\s-1$HOME\s+1/\f3.\fPprofile
.br
/tmp/sh\(**
.br
/dev/null
.SH SEE ALSO
cat(1),
cd(1),
chmod(1),
cut(1),
echo(1),
emacs(1),
env(1),
gmacs(1),
newgrp(1),
stty(1),
test(1),
umask(1),
vi(1),
dup(2),
exec(2),
fork(2),
ioctl(2),
lseek(2),
paste(1),
pathconf(2),
pipe(2),
sysconf(2),
umask(2),
ulimit(2),
wait(2),
rand(3),
a.out(5),
profile(5),
environ(7).
.PP
Morris I. Bolsky and David G. Korn,
.IR "The New KornShell Command and Programming Language" ,
Prentice Hall, 1995.
.PP
.I "POSIX \- Part 2: Shell and Utilities,"
IEEE Std 1003.2-1992, ISO/IEC 9945-2, IEEE, 1993.
.SH CAVEATS
.PP
If a command
is executed, and then a command with the same name is
installed in a directory in the search path before the directory where the
original command was found, the shell will continue to
.I exec
the original command.
Use the
.B \-t
option of the
.B alias
command to correct this situation.
.PP
Some very old shell scripts contain a
.B ^
as a synonym for the pipe character
.BR \(bv .
.PP
Using the
.B hist
built-in command within a compound command will cause the whole
command to disappear from the history file.
.PP
The built-in command \f3\|.\fP \f2file\^\fP
reads the whole file before any commands are executed.
Therefore,
.B alias
and
.B unalias
commands in the file
will not apply to any commands defined in the file.
.PP
Traps are not processed while a job is waiting for a foreground process.
Thus, a trap on
.B CHLD
won't be executed until the foreground job terminates.
.PP
It is a good idea to leave a space after the comma operator in
arithmetic expressions to prevent the comma from being interpreted
as the decimal point character in certain locales.
